Chemical Physics Letters (v.484, #4-6)

Contents (iii-xviii).

How do electrons break disulfide and N–Cα bonds in peptides in ECD/ETD mass spectrometry?This Letter reviews efforts made to elucidate the mechanism by which electron-capture and electron-transfer dissociation bond cleavages occur in mass spectrometry. The primary issues include where in the parent ion the electron initially attaches, whether the energy released in this initial electron-capture step is key to determining which bonds will cleave, whether the electron can migrate from the site to which it initially attaches to other sites in the parent ion, and, if so, over what distances and at what rates, and why, in polypeptides, one finds disulfide and N–Cα bond cleavage primarily.

Measuring the transport property of ZnO tetrapod using in situ nanoprobes by Yudong Gu; Jun Zhou; Wenjie Mai; Ying Dai; Gang Bao; Zhong Lin Wang (96-99).
The electrical transport characteristic of a ZnO tetrapod has been measured by in situ nanoprobes. By contacting the three legs of a tetrapod as the ‘gate’, source and drain, some control and tunability have been achieved in the output voltage/current, in analogous to the operation of a field effect transistor. A simple logic circuit has also been demonstrated.The electrical transport characteristic of a ZnO tetrapod has been measured by in situ nanoprobes. By contacting the three legs of a tetrapod as the ‘gate’, source and drain, some control and tunability have been achieved in the output voltage/current, in analogous to the operation of a field effect transistor. A simple logic circuit has also been demonstrated.

Silicon nanocrystals as matrix material for the desorption of biomolecule–water complexes by Marco Arold; François Piuzzi; Cornelia Jäger; Friedrich Huisken (100-103).
Using silicon nanocrystals with hydrated oxide shell as matrix material for biomolecules in laser desorption experiments, efficient formation of biomolecule–water complexes is observed.A new technique for the efficient production of biomolecule–water complexes, which may be employed in mass spectrometry and laser spectroscopy experiments, is described. Using native oxidized silicon nanocrystals as matrix material for biomolecules in laser desorption experiments, an enhanced efficiency for the formation of biomolecule–water complexes is observed. It is found that the water molecules are supplied by the silicon oxide shells covering the silicon nanocrystals. The new technique is demonstrated for the formation of tryptophan–water complexes with up to six water molecules.

Spin-birefringence in molecular currents: Tellurium and gold complexes by Amlan K. Roy; Joseph L. Speyer; Lizette Bartell; Daniel Neuhauser (104-109).
We use extended Hückel theory to simulate the spin-flip current and transmission function through rings containing elements with spin–orbit interactionWe simulate the spin-flip current and transmission function through rings containing elements with a spin–orbit interaction. In a previous study (J. Chem. Phys. 123 (2005) 204714) we predicted that such a system can show spin-birefringence, i.e., a spin current polarized parallel to the molecular axis can flip its direction due to a phase lag due to the spin–orbit interaction. Here we demonstrate the effect in a semi-empirical extended Hückel theory (EHT) molecular simulation. The ring systems studied are naphthalene–bitellurium, gold–porphyrin, and cyclometallated chlorogold, connected to polyacetylene.

Barium monoxide, BaO, molecule with dipole moment indicated.The optical Stark spectrum of the A 1Σ–X 1Σ+(0, 0) band of BaO was recorded and analyzed to determine the permanent electric dipole moments, μ, for the A 1Σ(ν  = 0) and X 1Σ+(ν  = 0) states to be 3.125(16) D and 7.869(17) D, respectively. The molecular beam electric resonance data for the X 1Σ+(ν  = 0) states [L. Wharton, M. Kaufman, W. Klemperer, J. Chem. Phys. 37 (1962) 621] was re-analyzed to produce μ of 7.9530(4) D. The systematic difference between the MBER and optical Stark values is discussed.

Photolytic induced processes in amyl nitrite – the predissociative bond breakage.The mechanistic aspects of the photo induced reactions of gaseous amyl nitrite have been investigated using ab initio calculations. We show that the C5H11O–NO bond dissociation mechanism is different on the S1 and S2 surfaces, respectively. The subsequent conformational changes in the ground state 1-pentoxy radical involves several barriers. Interestingly, we show that the intramolecular 1,5-H transfer in the 1-pentoxy radical proceeds in the opposite direction on the S1 state compared to the S0 reaction. Moreover, the results show that the excited state reaction of the alkoxy radical may be a proton transfer that proceeds on a repulsive surface.

Hydrogen migration and C–C bond breaking in 1,3-butadiene in intense laser fields studied by coincidence momentum imaging by Huailiang Xu; Tomoya Okino; Katsunori Nakai; Kaoru Yamanouchi; Stefan Roither; Xinhua Xie; Daniil Kartashov; Markus Schöffler; Andrius Baltuska; Markus Kitzler (119-123).
The hydrogen atom bonded originally to one of the two central carbon atoms in 1,3-butadiene in intense laser fields migrates preferentially to its neighboring terminal carbon atom site, which leads to a change in the bond energies of the central C–C bond and the side C–C bond.Two-body dissociation processes of H2C=CH–CH= CH 2 2 + induced by an intense laser field were investigated by the coincidence momentum imaging method. Four dissociation pathways, C 4 H 6 2 +  → CH2 +  +  C 3 H 4 + , C 4 H 6 2 +  → CH3 +  +  C 3 H 3 + , C 4 H 6 2 +  →  C 2 H 3 +  +  C 2 H 3 + and C 4 H 6 2 +  →  C 2 H 2 +  +  C 2 H 4 + , were identified. The existence of the second and fourth pathways can be regarded as evidences of the chemical bond rearrangement processes associated with hydrogen migration in the intense laser field. It was found that the hydrogen atom bonded originally to one of the two central carbon atoms migrates preferentially to its neighboring terminal carbon atom site.

Interaction of N2 with Kr: Potential energy surface and bound states by Zhongquan Wang; Mei Niu; Eryin Feng; Haijun Yu; Jianming Du; Jianguo Ma (124-129).
The first two-dimensional ab initio interaction potential energy surface of the Kr–N2 complex is developed by CCSD(T) method.The first ab initio potential energy surface of the Kr–N2 complex is developed using CCSD(T) method. A mixed basis sets, aug-cc-pVQZ for the C and O atom, and aug-cc-pVQZ-PP for the Kr atom, with an additional (3s3p2d2f1g) set of midbond functions are used. The potential has a minimum of −111.79 cm−1 with R e  = 7.30a 0 at T-shaped geometry (θ e  = 90°). Based on the potential, the bound state energies are calculated up to J  = 5 for seven isotopomers of 84Kr–14N2, 86Kr–14N2, 82Kr–15N2, 84Kr–15N2, 86Kr–15N2, 86Kr–14N15N, 84Kr–14N15N complex. Compared with available experimental data, all predicted transition frequencies agree within better than 2% with the experimental results.

Theoretical treatment of state-selective one-electron capture by Mg2+ ions in collision with Zn by M. Amami; A. Zaidi; S. Lahmar; M.C. Bacchus-Montabonel (130-133).
Potential energy curves and coupling matrix elements of the one-electron capture by Mg2+ ions in collision with Zn atoms have been determined at the multi-reference configuration interaction level of theory. The cross sections calculated using a semi-classical approach in the [1–300] keV laboratory energy range are in good agreement with the experimental measurements and reflect the importance of the molecular description.Total and partial cross sections for the Mg2+(2p6) + Zn(4s2) collision system.Potential energy curves and coupling matrix elements of the one-electron capture by Mg2+ ions in collision with Zn atoms have been determined at the multi-reference configuration interaction level of theory. The cross sections calculated using a semi-classical approach in the [1–300] keV laboratory energy range are in good agreement with the experimental measurements and reflect the importance of the molecular description.

The location of the energy minimum of the potential energy curves for proton motion in the intermolecular hydrogen bonds in phenol–tertiary amine complexes depends on the proton donor and proton acceptor properties of the complex components and also on the substituent effects in phenol ring as well as the different proton acceptors.The potential energy curves for proton motion in the intermolecular hydrogen bonds in phenol–tertiary amine complexes have been analyzed to investigate the location of the energy minimum. The proton donor and proton acceptor properties of the complex components are the main parameters which determine the location of the minimum. Also substituent effect in phenols as well as the different proton acceptors can shift the potential energy curve for proton motion against the reaction coordinate.

Theoretical study of Ar–MCO (M = Pd, Pt) by Yuriko Taketsugu; Takeshi Noro; Tetsuya Taketsugu (139-143).
QCISD(T)/DK3 calculations show that Ar atom is bound to PdCO and PtCO with super-strong van der Waals interaction.Ab initio calculations are performed for noble-gas complexes, Ar–PdCO and Ar–PtCO, by QCISD(T) with a Douglas–Kroll relativistic scheme. The electronic ground states of Ar–PdCO and Ar–PtCO are predicted to be 1Σ with linear equilibrium structure, and the binding energy of Ar is estimated as 5.3 and 8.2 kcal/mol for Ar–PdCO and Ar–PtCO, respectively. The M–C–O (M = Pd, Pt) bending frequency in MCO increases by ∼10% in Ar–MCO. The present calculations suggest that the experimentally reported M–C–O bending frequencies for MCO measured in the solid argon matrix are possibly to be assigned to the overtone band of the M–C–O bending mode of Ar–MCO.

Theoretical study on icosahedral water clusters by Oleksandr Loboda; Vladyslav Goncharuk (144-147).
A new concept of viewing icosahedral cluster as expansion of dodecahedral subvolumes.Here we present a structural study of different gas hydrates using the B3LYP hybrid DFT exchange-correlation functional. A new concept for viewing the icosahedral cluster as an expansion of dodecahedral subclusters is introduced. The investigated structures consist of 280 water molecules. Structural and orientational features of various guest molecules occupying the central cavity of the clusters are established. It was found that water as the guest molecule has the highest stabilization energy in studied clusters. The conformational changes in dimer and trimer water molecules upon incorporation into hydrate cavity are discussed. The influence of second- and third-order solvent shells is illustrated on example of icosahedral water cluster derivatives.

Tensor cross sections and collisional depolarization of MgH by He atoms by K. Hammami; N. Jaidane; N. Feautrier; A. Spielfiedel; F. Lique (148-153).
Typical energy variation of the tensor and elastic depolarization cross sections of MgH in collision with Helium.Tensor cross sections for collisions of MgH ( X 2 Σ + ) molecule with helium atom are computed using a new accurate ab initio potential energy surface calculated at the RCCSD (T) level. In the calculations, the MgH bond length is fixed at its experimental value (3.269 bohr). Basis set superposition error is corrected and bond functions are placed at mid-distance between the MgH mass centre and the He atom, for a better description of the van der Waals interaction. The global minimum of the PES is 12.2 cm - 1 . State-to-state tensor and depolarization cross sections are calculated. The tensor cross sections and depolarizing cross sections are computed for kinetic energies up to E c ⩽ 1000 cm - 1 . The tensor cross sections are found to decrease with increasing values of K.

‘Relativistic bond’ in complexes of Cu, Ag, and Au elements with phosphine by Jaroslav Granatier; Miroslav Urban; Andrzej J. Sadlej (154-159).
CCSD(T) DKH calculations of binding energies of CuPH3, AgPH3, and AuPH3 complexes. Relativistic effects are crucial in explaining the bonding mechanism.The binding energies in CuPH 3 , AgPH 3 , and AuPH 3 complexes, as determined from one-component (scalar) CCSD(T) calculations with aug-cc-pVTZ basis set, are 32.9, 11.5, and 66.7 kJ/mol, respectively. The large binding energy in AuPH 3 is essentially due to relativistic effects. On neglecting them the interaction between Au and the lone-electron pair of PH 3 results in a weak van der Waals complex. The bonding in M ⋯ PH 3 complexes is interpreted in terms of the charge transfer from the electron lone-pair of PH 3 to the metal atom. In AuPH 3 this mechanism is supported by the large relativistic increase of the Au electron affinity.

Kinetic study of the reaction of the acetyl radical, CH3CO, with O3 using cavity ring-down spectroscopy by Tomasz Gierczak; B. Rajakumar; Jonathan E. Flad; James B. Burkholder (160-164).
The reaction of the acetyl radical, CH3CO, with O3 studied using pulsed laser photolysis combined with cavity ring-down spectroscopy.Rate coefficients for the gas-phase reaction CH3CO + O3  → products were measured between 248 and 403 K at 60–200 Torr (N2). Rate coefficients were measured under pseudo-first-order conditions in CH3CO with CH3CO produced by 248 nm pulsed laser photolysis of acetone and monitored using cavity ring-down spectroscopy at 532 nm. Rate coefficients were found to be pressure independent with a weak negative temperature dependence k 1 ( T ) = 1.50 - 0.30 + 0.25 × 10 - 11 exp [ ( 300 ± 50 ) / T ] cm 3 molecule - 1 s - 1 and k 1(296 K) = (4.4 ± 0.5) × 10−11  cm3  molecule−1  s−1 where the quoted uncertainties are 2σ and include estimated systematic errors.

The interaction of Kr(1S) +  O 2 + (X 2Πg) leads to the formation of weakly bound Kr O 2 + ion complexes of X ˜ 2A″ and A ˜ 2B2 symmetries.High level ab initio RCCSD(T) calculations were used to explore the X ˜ 2A″ and A ˜ 2A′ potential energy surfaces stemming from the interaction of Kr(1S) with the O 2 + (X 2Πg) molecular cation. On both surfaces weakly bound Kr O 2 + complexes were found, namely Kr O 2 + ( X ˜ 2A″) and Kr O 2 + ( A ˜ 2B2), with D e(D 0) = 0.240 (0.223) and 0.135 (0.126) eV, respectively. Potential energy curves, slices of the X ˜ 2A″ and A ˜ 2A′ surfaces, are also presented.

Ratiometric spectroscopic response of pH sensitive probes: An alternative strategy for multidimensional sensing by Deboleena Sarkar; Arabinda Mallick; Basudeb Haldar; Nitin Chattopadhyay (168-172).
An alternative strategy, hybridizing the proper choice of a pH sensitive fluorophore and the ratiometric technique of plot of the spectral parameters of the probe, has been introduced for the generation of new molecular sensors for multidimensional sensing purposes. Selectivity factor is found to depend on the dissociation constant of the conjugate acid of the anion to be detected. The technique can be exploited for the sensing of cyanide ion, accurate to the micromolar level of concentration.An alternative strategy, hybridizing the proper choice of a pH sensitive fluorophore and the ratiometric technique of plot of the spectral parameters of the probe, has been introduced for the generation of new molecular sensors for multidimensional purposes. Various anions present in aqueous medium or biological fluids through alkali metal salts, can be detected and estimated. Selectivity factor turns out to be dependent on the dissociation constant of the conjugate acid of the anion to be detected. The technique can be exploited for the sensing of cyanide ion, a supremely toxic anion, accurate to the micromolar level of concentration.

Polarization electrostatic effects on alkane hydration in water.We present a refined alkane charge equilibration (CHEQ) force field, improving our previously reported CHEQ alkane force field to better reproduce experimental hydration free energies. Experimental hydration free energies of ethane, propane, butane, pentane, hexane, and heptane are reproduced to within 3.6% on average. We demonstrate that explicit polarization results in a shift in molecular dipole moment for water molecules associated with the alkane molecule. We also show that our new parameters do not have a significant effect on the alkane–water interactions as measured by the radial distribution function (RDF).

A highly efficient alternating photocurrent in the thin films of interacting organic–radical dimers can be induced by a modulated light, which can be ascribed to bulk polarization and an imbalance between hole and electron mobilities and bulk polarization.Thin films of interacting dimers of 4,4′-bis(1,2,3,5-dithiadiazolyl), sandwiched by ITO and Al, exhibit an anomalous transient current, due to a significant imbalance between the hole and electron mobilities and bulk polarization. We propose a new operational principle for organic optoelectronic conversion systems, which efficiently generates alternating photocurrent without being affected by the disadvantages of organic materials, such as poor mobility.

The temperature dependence of the R1 line in ruby is revisited by employing transient spectral hole-burning.Transient spectral-hole-burning studies of the R1(±3/2) line ( E ¯ (2E) ←  4A2(±3/2)) in 20 ppm ruby were conducted between 2.4 and 50 K in a low magnetic field (B|| = 9.15 mT) and the results were supplemented with the original data of McCumber and Sturge. A direct one-phonon process, 2 A ¯ ← E ¯ , is the main contribution to the linewidth up to 50 K whereas at higher temperatures two-phonon Raman scattering becomes dominant. The two processes are well described by Δ Γ direct = Γ 0 / ( exp ( Δ / k B T ) - 1 ) and a non-perturbative expression for the electron–phonon interaction developed by Hsu and Skinner. The value of Γ 0  = 141 (±4) MHz is in excellent agreement with the result of 142 ± 6 MHz previously obtained for the R2 line.

Solvent effects on the electronic absorption spectrum of camphor using continuum, discrete or explicit approaches by Jacob Kongsted; Benedetta Mennucci; Kaline Coutinho; Sylvio Canuto (185-191).
The effect of solvation on the lowest electronic excitation energy of camphor is studied using either implicit, discrete or explicit solvation models.We address the effect of solvation on the lowest electronic excitation energy of camphor. The solvents considered represent a large variation in-solvent polarity. We consider three conceptually different ways of accounting for the solvent using either an implicit, a discrete or an explicit solvation model. The solvatochromic shifts in polar solvents are found to be in good agreement with the experimental data for all three solvent models. However, both the implicit and discrete solvation models are less successful in predicting solvatochromic shifts for solvents of low polarity. The results presented suggest the importance of using explicit solvent molecules in the case of nonpolar solvents.

Single molecule diffusion at step edges by Arne Schob; Frank Cichos (192-196).
Single dye molecule diffusion trajectories at a mica step edge.We have tracked the motion of single Rhodamine 123 molecules in tetrakis-(2-ethylhexoxy)-silane close to a microscopic surface step on freshly cleaved mica sheets. Introducing a local directional measure of the mobility of single molecules we are able to unravel the anisotropy of single molecule diffusion close to the surface step. Direct comparison of the experimental results with theoretical calculations reveals a strong effective trapping potential on the order of a few 100 meV. This potential confines molecular motion into a thin layer close to the step surface, in which the mobility of molecules is slowed down by one order of magnitude as compared to the flat surface.

Sn etching with hydrogen radicals to clean EUV optics by M.M.J.W. van Herpen; D.J.W. Klunder; W.A. Soer; R. Moors; V. Banine (197-199).
We demonstrate that we can clean EUV optics from Sn contamination using etching with hydrogen radicals at >50 nm/min etch rate.Extreme ultraviolet (EUV) collector optics are an essential part of EUV lithography machines, but are subject to substantial Sn contamination.We demonstrate a method to clean EUV optics from Sn contamination. We use hydrogen radicals to remove Sn at >50 nm/min etch rate. For a Ru surface, the Sn etch rate drops with two orders of magnitude when the Sn layer becomes thinner.We found that a very thin (∼2 nm) layer of Si3N4 between the Sn and the Ru layer increases the Sn etch rate to its maximum value.Finally, we have demonstrated that this technique may be used to fully recover the reflectivity of Sn-contaminated EUV mirrors.

EPR and optical absorption studies on VO2+ ions in calcium fumarate trihydrate single crystals by Ram Kripal; Indrajeet Mishra; S.K. Gupta; Manju Arora (200-206).
EPR and optical studies of VO2+ doped calcium fumarate trihydrate are done and nature of bonding is discussed.Electron Paramagnetic Resonance (EPR) studies of VO2+ ions in calcium fumarate trihydrate single crystals have been done at room temperature. EPR analysis indicates the presence of two magnetically inequivalent VO2+ sites. For the two sites the spin Hamiltonian parameters are, Site I: gx  = 1.9689, gy  = 2.0087, gz  = 1.9344, Ax  = 73, Ay  = 88, Az  = 202; Site II: gx  = 1.9675, gy  = 2.0100, gz  = 1.9346, Ax  = 75, Ay  = 90, Az  = 206 (×10−4) cm−1. The optical absorption study is also carried out at room temperature. By correlating EPR and optical data the nature of bonding in the crystal is discussed. The three-line superhyperfine structure has been attributed to two protons.

NIR fluorescence and visible upconversion studies of Nd3+ ions in calcium fluoroborate glasses by J. Suresh Kumar; A. Mohan Babu; T. Sasikala; L. Rama Moorthy (207-213).
Energy level diagram showing normal and upconversion fluorescence processes along with cross-relaxation channels in Nd3+:CFB glasses.This Letter reports on the preparation, optical absorption, NIR fluorescence and visible upconversion studies of neodymium doped calcium fluoroborate (CFB) glasses. The title glasses were prepared by melt quenching technique and the phonon energy of the host glass was estimated by the FTIR spectrum. Radiative parameters of various transitions/levels were calculated by applying Judd–Ofelt (J–O) theory. The concentration dependence of NIR emission and visible upconversion intensities from the 4F3/2 and 2D3/2 levels has been discussed. Decrease of experimental lifetime of 4F3/2 level with concentration has also been discussed by recording decay curves of the NIR emission.

Pulsed-jet discharge matrix isolation and computational study of CX2Br+ (X = H, F) by Lisa George; Aimable Kalume; Scott A. Reid (214-218).
Experimental schematic of the pulsed-jet discharge matrix isolation technique.Pulsed-jet discharge matrix isolation spectroscopy and computational methods were used to characterize the CX2Br+ (X = H, F) ions. Our experiments combined matrix isolation techniques with a pulsed DC discharge nozzle, where a dilute CX2Br2:Ar sample was discharged and the products deposited onto a KBr window held at ∼8 K. This study represents the first spectroscopic observation of CH2Br+, and the first report of the C–Br stretching frequency of CF2Br+. Our results suggest that the primary mechanism for ion formation is ionization/fragmentation of the precursor by collision with metastable rare gas (Ar) atoms.

Thermal conductivity and interfacial energies of solid Sn in the Sn–Cu alloy by Y. Kaygısız; Y. Ocak; S. Aksöz; N. Maraşlı; K. Keşlioğlu; E. Çadırlı; H. Kaya (219-224).
The thermal conductivity, Gibbs–Thomson coefficient and interfacial energies of solid Sn in the Sn–Cu alloy have been determined.The equilibrated grain boundary groove shapes of solid Sn in equilibrium with the Sn–Cu eutectic liquid were observed from a quenched sample. The Gibbs–Thomson coefficient, solid–liquid interfacial energy and grain boundary energy of solid Sn have been determined to be (8.7 ± 0.6) × 10−8  Km, (113.1 ± 13.6) × 10−3  J m−2 and (222.4 ± 28.9) × 10−3  J m−2, respectively. The thermal conductivity of solid phase and the thermal conductivity ratio of liquid phase to solid phase for Sn–1.3 at.%Cu alloy have also been measured with radial heat flow apparatus and Bridgman type growth apparatus, respectively.

Study of transient thermal lensing effect in C60-toluene solution by Che-Kai Chang; Chang-Chi Leu; Tai-Huei Wei; Sidney Yang; Tzer-Hsiang Huang; Yinglin Song (225-230).
The schematic of the five-energy-model (S0, S1, S2, T1, and T2) model for C60.Using the Z-scan technique and a 532 nm TEM00 mode laser pulse with a width of 2.8 ns and a waist radius of 15.0 μm, we characterize photo absorption induced thermal lensing effect in a toluene solution of C60. To fit the experimental results, we have to strictly solve the thermal acoustic wave equation, driven by the temperature rise, to achieve the solvent density change. Steady state (instantaneous expansion) approximation of this wave equation greatly breaks the agreement of the theoretical simulation with the experimental results. Accordingly, the experimentally observed thermal lensing effect is assured in the transient regime.

Supporting metal atoms on a metal oxide increases their reactivity towards oxygen.The influence of a metal oxide support on the reactivity of adsorbed metals is a key question in surface reactivity and heterogeneous catalysis. Density functional theory (DFT) calculations are used here to examine support effects on one diagnostic of reactivity, oxygen binding, for Pd, Pt, Ag, and Au atoms supported on two representations of an α-alumina surface. Supported metal atoms uniformly bind oxygen more strongly than unsupported ones, so that even supported Au exothermically binds O. Further, oxygen adsorption is enhanced on a hydroxylated support by spillover of H from support to M–O bond.

The electronic transparency of a single CO molecule at contact by Abir De Sarkar; Francisco Ample; Christian Joachim (237-241).
Searching for the good electronic contact point on a single CO molecule in a STM tunnel junction.At the exact contacting distance of a CO molecule inserted in the tunnel junction between a Cu(3 1 1) surface and an STM tip, it is demonstrated that the calculated conductance of a single CO is smaller (G  = 6 × 10−4 G o with G o  = 2e2/h) than the corresponding vacuum junction conductance. This is not due to a destructive interference between tunnel channels through the junction but owing to the very large CO–Cu(3 1 1) electronic coupling which desequilibrates the electronic structure of the tunnel junction. A molecule chemisorbed on at least one of its contacting electrodes is not a guaranty for a large junction conductance.

Strong nonlinear photonic responses from microbiologically synthesized tellurium nanocomposites by Kang-Shyang Liao; Jun Wang; Sampath Dias; James Dewald; Nigel J. Alley; Shaun M. Baesman; Ronald S. Oremland; Werner J. Blau; Seamus A. Curran (242-246).
The microbiologically synthesized tellurium nanorod/polymer composites exhibit excellent broadband optical limiting responses at 532 and 1064 nm.A new class of nanomaterials, namely microbiologically-formed nanorods composed of elemental tellurium [Te(0)] that forms unusual nanocomposites when combined with poly(m-phenylenevinylene-co-2,5-dioctoxy-phenylenevinylene) (PmPV) is described. These bio-nanocomposites exhibit excellent broadband optical limiting at 532 and 1064 nm. Nonlinear scattering, originating from the laser induced solvent bubbles and microplasmas, is responsible for this nonlinear behavior. The use of bacterially-formed Te(0) when combined with an organic chemical host (e.g., PmPV) is a new green method of nanoparticle syntheses. This opens the possibilities of using unique, biologically synthesized materials to advance future nanoelectronic and nanophotonic applications.

Preparation and properties of graphene nanosheets–polystyrene nanocomposites via in situ emulsion polymerization by Huating Hu; Xianbao Wang; Jingchao Wang; Li Wan; Fangming Liu; Han Zheng; Rong Chen; Chunhui Xu (247-253).
Graphene nanosheets–polystyrene (GNS–PS) nanocomposites were prepared by in situ emulsion polymerization and reduction of graphene oxide using hydrazine hydrate.Graphene nanosheets–polystyrene nanocomposites were prepared by in situ emulsion polymerization and reduction of graphene oxide using hydrazine hydrate. PS microspheres covalently linked to the edges of graphene nanosheets. The polystyrene-absorbed graphene has been dispersed well in the solvents of toluene and chloroform. The nanocomposites display high electrical conductivity, and a considerable increase in glass-transition temperature and good thermal stability of PS are also achieved. The facile and environmental-friendly technique presented here is an effective and promising method of functionalization of graphene sheets by polymers or other compounds.

Effect of polymeric stabilizers on the catalytic activity of Pt nanoparticles synthesized by laser ablation by Dae Keun Park; Seung Jun Lee; Joon-Hwa Lee; Myong Yong Choi; Sang Woo Han (254-257).
The net charge of the stabilizers plays a decisive role for the nanoparticle-mediated electron transfer between charged reactants.The effect of polymeric stabilizers on the catalytic activity of Pt nanoparticles for an electron-transfer reaction between Fe ( CN ) 6 3 - and S 2 O 3 2 - was investigated. Pt nanoparticles were prepared by laser ablation of Pt plate in water, and then stabilized with typical stabilizing polymers such as poly(vinyl pyrrolidone) (PVP), poly(vinyl sulfate) (PVS), and polyethyleneimine (PEI). The catalytic reaction proceeds much faster with PEI-stabilized nanoparticles than PVP- or PVS-stabilized particles. The activity of nanoparticles also highly depends on pH and polymer concentration. These clearly demonstrate that the net charge of the stabilizers plays a decisive role for the nanoparticle-mediated electron transfer between charged reactants.

Single-charge tunneling in uncoupled boron-doped silicon nanochains by D.D.D. Ma; K.S. Chan; D.M. Chen; S.T. Lee (258-260).
A semiconducting B-doped Si ‘island’ surrounded by insulating oxide can control and measure the movements of single electrons.Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements have been performed on boron-doped silicon nanochains (BDSNs). STM results suggest BDSNs may be an excellent nanostructure to build single-charge tunneling transistors. STS measurements clearly reveal Coulomb blockade (CB) effects in BDSN at 25 K with a large charging energy, which should make CB effect observable even at RT. The CB characteristics are attributed to boron- or impurity-induced local states at the surface or interface. The experimental results suggest the possibility of realizing single-charge nanodevices by exploiting boron- or defect-induced charge trapping and de-trapping processes at the nanoparticles of BDSNs.

The vibrational satellites in the low-temperature emission of Pt(4,6-dFppy)(acac) can be tuned from a vibronically to a Franck–Condon induced structure by high magnetic fields.Effects of high magnetic fields on the properties of the lowest triplet state of the OLED emitter Pt(4,6-dFppy)(acac) are studied by site-selective high-resolution optical spectroscopy. Application of high fields strongly alters the pattern and magnitude of splitting of the triplet term, the oscillator strengths of the purely electronic 0–0 transitions between the T1 substates and the singlet ground state, and the vibrational satellite structures. In particular, the mechanism of radiative vibrational deactivation of the lowest triplet substate I changes with increasing field from a vibronically induced (Herzberg–Teller) to a Franck–Condon induced mechanism.

Effects of dopant and defect on the adsorption of carbon monoxide on graphitic boron nitride sheet: A first-principles study by Yong-Hui Zhang; Kai-Ge Zhou; Xin-Chun Gou; Ke-Feng Xie; Hao-Li Zhang; Yong Peng (266-270).
Functionalizing graphitic boron nitride sheet by Al-dopant and various defects was investigated using CO as a probe molecule.The inert surface of graphitic boron nitride sheet (g-BN) hinders the application of this new nanomaterial in electronic devices. Herein, we exploited the possibilities of functionalizing g-BN by introducing Al-dopant and defects (Stone–Wales or vacancy), and studied the interactions between the modified g-BN and CO molecule. The doped and defective g-BN exhibit much higher affinities with the probe molecule than pristine g-BN. The vacancy-defected g-BN shows narrower band gap and spontaneous magnetization upon CO adsorption. These results may help to seek appropriate chemical modification methods to widen the application fields of the g-BN nanomaterials.

The synthesis of Au nanotriangles in presence of cetyltrimethyl ammonium cetyltrimethyl ammonium bromide by reducing Au3+ ions with tryptophan is reported. Interestingly, intense white light emission associated with enhanced fluorescence of oxidized tryptophan adsorbed on the tips of the Au triangles was observed. These results are supported by lifetime measurements and fluorescence.We report the synthesis of Au nanoparticles in presence of two surfactants cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB) by reducing Au3+ ions with tryptophan. Interestingly, triangular shaped particles were seen to form in presence of CTAB, while spherical nanoparticles resulted with CTAC. The highlight of this result is the white light emission from the Au triangles obtained when CTAB is used. These results are supported by lifetime measurements and fluorescence.

Wannier analysis of magnetic graphenes by Masashi Hatanaka (276-282).
Ferromagnetic interactions in graphenes with methylene edges were deduced from Wannier functions of nonbonding crystal orbitals.The spin alignment in graphenes with methylene edges is deduced using the crystal orbital method. The ferromagnetic interactions result from exchange integrals between Wannier functions of nonbonding crystal orbitals, in which the amplitudes are localized at the edges. The exchange integral per unit cell decreases as the number of ladders increases.

Modification of the electrical properties of PEDOT:PSS by the incorporation of ZnO nanoparticles synthesized by laser ablation by N.G. Semaltianos; S. Logothetidis; N. Hastas; W. Perrie; S. Romani; R.J. Potter; G. Dearden; K.G. Watkins; P. French; M. Sharp (283-289).
ZnO nanoparticles were synthesized by using the easy, fast and environmentally friendly method of laser ablation. The colloidal solution of the nanoparticles was mixed with PEDOT:PSS and the resulting nanocomposite has electrical conductivity higher by almost twice as compared with the polymer.Laser ablation of a solid target in a liquid environment offers an easy, fast, and environmentally friendly method for the generation of nanoparticles with desired properties. In this Letter we report modification of the electrical properties of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)) by the incorporation into it of ZnO nanoparticles which were synthesized by laser ablation. By forming the nanocomposite, change of the chemical structure of the polymer from a mixture of benzoid and quinoid to a mostly quinoid and a conformational change of the polymer chains from coil to expanded-coil or linear was observed. Furthermore, these changes result in an increase by almost twice of the electrical conductivity of the polymer.

1D polyvinylidene difluoride–single-wall carbon nanotubes nanocomposites are fabricated via anodized alumina template by infiltration of the mixture at temperatures above the blend molten temperature. Presence and distribution of the single-wall carbon nanotubes all the way along PVDF nanorods is proven by confocal Raman spectroscopy.Novel single-wall carbon nanotubes/polyvinylidene difluoride one-dimensional nanorods, have been prepared via anodized alumina template by infiltration of the mixture at temperatures above the blend molten temperature. By combining X-ray diffraction and Raman spectroscopy techniques, the latter working on confocal mode, it has been shown, for the first time, the presence and distribution of carbon nanotubes all the way along the nanorod length, ∼50 μm. The maximum concentration of single-wall carbon nanotubes is found within the first 15 μm. These 1D nanostructured materials could have potential applications in electronic, optical, magnetic, and energy storage devices.

The PM3 method, with dispersive corrections, is shown to accurately predict the interaction energy of nucleic acid bases with graphene and carbon nanotubes.The accuracy of the semiempirical molecular orbital method PM3 with dispersive corrections (PM3-D, PM3-D∗), for computing the interaction energy of nucleic acid bases with graphene and single-wall carbon nanotubes has been assessed by comparison with dispersion corrected density functional theory (DFT-D) and with MP2 data. This semiempirical approach is shown to be considerably more accurate and cost effective than many pure density functionals.

Evidence of pentacene bulk and thin film phase transformation into an orthorhombic phase by iodine diffusion by R. Srnanek; J. Jakabovic; E. Dobrocka; G. Irmer; U. Heinemeyer; K. Broch; F. Schreiber; A. Vincze; V. Machovic; J. Kovac; D. Donoval (299-303).
We present evidence of pentacene bulk and thin film phase transformation into an orthorhombic phase by iodine diffusion and vacuum annealing.We present evidence for 130 nm thick pentacene films ordered in the orthorhombic phase obtained by iodine diffusion into the film deposited by classical thermal evaporation. After desorption of iodine by vacuum annealing the crystallographic properties of the investigated pentacene films resemble those of very thin thermal evaporated films that exhibit an orthorhombic phase with high electrical performance. Therefore, the results presented in this work are believed to be important for the development of organic field-effect transistors.

Measuring the SERS enhancement factors of dimers with different structures constructed from silver nanocubes by Pedro H.C. Camargo; Leslie Au; Matthew Rycenga; Weiyang Li; Younan Xia (304-308).
This Letter describes a systematic investigation on the SERS enhancement factors for dimers constructed from two sharp Ag nanocubes presenting a variety of well-defined structures.We describe a systematic investigation on the SERS enhancement factors of individual dimers (EF dimer ) constructed from two Ag nanocubes that display a face-to-face, edge-to-face, or edge-to-edge structure. The highest field-enhancements were obtained for the dimers displaying a face-to-face and edge-to-face configuration. In these two systems, EF dimer was insensitive the dimer geometry and corresponded to 2.0 × 107 and 1.5 × 107, respectively. However, EF dimer was decreased to 5.6 × 106 for the edge-to-edge structure. These variations in the detected field-enhancements could be explained based on the relative orientation of the nanocubes and the number of probe molecules enclosed in the hot-spot region for each dimer configuration.

Solution state hybridization detection using time-resolved fluorescence anisotropy of quantum dot-DNA bioconjugates by Gerard Giraud; Holger Schulze; Till T. Bachmann; Colin J. Campbell; Andrew R. Mount; Peter Ghazal; Mizanur R. Khondoker; Stuart W.J. Ember; Ilenia Ciani; Chaker Tlili; Anthony J. Walton; Jonathan G. Terry; Jason Crain (309-314).
Time-resolved anisotropy decays of quantum dots nanoparticles attached to single and double stranded DNA.In this Letter, we demonstrate the application of time-resolved fluorescence anisotropy measurements to detect solution state hybridization of streptavidin conjugate (CdSe)ZnS quantum dots (QD). The study was performed on samples containing 10 nM QD incubated with 800 nM DNA. We show that the rotational correlation time of QD–DNA constructs increases significantly upon hybridization with values of 330 ns (QD-ssDNA) and 1.3 μs (QD-dsDNA), corresponding to a diameter of 14 nm and 23 nm respectively. The present study opens a new modality for hybridization detection using quantum dots.

The critical exponent of the force needed to unzip DNA is proportional to the critical exponent of the specific heat.In this Letter, we investigate the link between thermal denaturation and mechanical unzipping for two models of DNA, namely the Dauxois–Peyrard–Bishop model and a variant thereof we proposed recently. We show that the critical line that separates zipped from unzipped DNA sequences in mechanical unzipping experiments is a power-law in the temperature-force plane. We also prove that for the investigated models the corresponding critical exponent is proportional to the critical exponent α, which characterizes the behaviour of the specific heat in the neighbourhood of the critical temperature for thermal denaturation.

Photochromic dye semi-intercalation into DNA-based polymeric matrix: Computer modeling and experiment by Grzegorz Pawlik; Antoni C. Mitus; Jaroslaw Mysliwiec; Andrzej Miniewicz; James G. Grote (321-323).
Illustration of the semi-intercalation of DR1 in a DNA–CTMA biopolymer showing the origin of memory effect of upon light excitation.We use the recently formulated hypothesis of semi-intercalation of an azo-dye Disperse Red 1 (DR1) into a biopolymeric material made of deoxyribonucleic acid (DNA) complexed with the cationic surfactant hexadecyltrimethyl-ammonium chloride (CTMA) to model the unique photochromic properties of the DR1:DNA–CTMA system. Kinetic Monte Carlo simulations accurately reproduce the main experimental results of laser dynamic inscription of diffraction gratings in this photochromic material: short response time, low diffraction efficiency, single-exponential kinetics and flat wavelength dependence.

Theoretical study on the absorption maxima of real GFPs by Azuma Matsuura; Tomohiko Hayashi; Hiroyuki Sato; Atsuya Takahashi; Minoru Sakurai (324-329).
The electron-density difference between the ground state and excited state of interest in the real GFP at INDO/S-CIS.The excited-state calculations for the real green fluorescent protein (GFP) and its mutants, including the wild-type GFP, Y66F, blue fluorescent protein, and cyan fluorescent protein, were carried out at the INDO/S-CIS//ONIOM (B3LYP/6-31G∗∗:AMBER) level. The numbers of singly excited configuration state functions at INDO/S-CIS were over 20 million. The calculated absorption maxima were in good agreement with the experimental data with a computational error of ⩽15 nm. For the wild-type GFP, INDO/S-CIS yielded a bathochromic shift of 38 nm with respect to its model chromophore in vacuo, which was also in good agreement with the extrapolated experimental shift of 45 nm.

1H NMR characterization of the intermediate formed upon UV-A excitation of biopterin, neopterin and 6-hydroxymethylpterin in O2-free aqueous solutions by Mariana Vignoni; M. Laura Salum; Rosa Erra-Balsells; Andres H. Thomas; Franco M. Cabrerizo (330-332).
For the three studied pterin derivatives the unstable red intermediate generated by UV-A irradiation under anaerobic conditions was identified by 1H NMR analysis, in alkaline D2O solutions, as 5,8-dihydro-6-formylpterin.Pterins belong to a family of heterocyclic compounds present in a wide range of living systems and participate in relevant biological functions. Under anaerobic conditions, the unstable red intermediate generated by UV-A irradiation of biopterin, neopterin and 6-hydroxymethylpterin was identified by 1H NMR analysis, in alkaline D2O solutions, as 5,8-dihydro-6-formylpterin.

Linearly polarized light absorption spectra of chlorosomes, light-harvesting antennas of photosynthetic green sulfur bacteria by Hitoshi Tamiaki; Shingo Tateishi; Shosuke Nakabayashi; Yutaka Shibata; Shigeru Itoh (333-337).
Polarized light absorption spectra of ellipsoid-shaped chlorosomes in a specially compressed polyacrylamide gel in the visible Soret region as well as the near-infrared Qy region provided useful information for supramolecular structures of bacteriochlorophyll self-aggregates in a chlorosome.Absorption spectra of chlorosomes isolated from several species of photosynthetic green sulfur bacteria using linearly polarized light were measured in a compressed polyacrylamide gel at three-dimensional geometric orientations. Chlorosomes containing self-aggregates of bacteriochlorophyll(BChl)-e gave two distinct Soret absorption peaks, which were assigned to By and Bx bands at longer and shorter wavelengths, respectively. The transition dipole of By band was determined to be parallel to the long axis of ellipsoid-shaped chlorosomes, while that of Bx parallel to the short axis. Analysis of linear dichroism and polarization degrees supported the above orientation, while the alignment of Bx transition dipoles was limited. The features are also observed in chlorosomes having BChls-c and d. The absorption bands in the Soret region by linearly polarized light are shown for the first time to be useful for the investigation of supramolecular structures of chlorosomal self-aggregates, as in the redmost Qy bands reported earlier.

Whole system solvated in water (rendered in MSMS) with periodic boundary conditions. The molecular model used for the SMD simulations consists of SP-D (rendered in NewCartoon) with saccharide ligands (rendered in CPK) and coordinated calcium ion (colored in green). Sodium and chloride ions are shown in yellow and pink. Virtual springs are attached to saccharides and the other end of spring links to a dummy atom to which external force is applied. The fixed atoms are colored in gray.Steered molecular dynamics (SMD) simulations were performed to investigate the dynamic characteristics in the unbinding process of α-d-glucose from human pulmonary surfactant protein D (SP-D). The result shows that the residues Glu321, Asp325, Glu329 and Arg343 are responsible for the different dynamic strength from the affinity in the stable state of thermodynamics. Especially the hydrogen bonds between the residues Glu321, Glu329 and glucose increase their interaction and contribute the counteraction to the external force. The change of the directions of the hydroxyl groups in the C2 and C6 atoms of α-d-glucose also affects the dynamic strength in the pulling procedure.

Improved accuracy by the restrained hybridization matrix in the GHO QM/MM method.We assess transformation matrices in the combined quantum mechanical and molecular mechanical method based on generalized hybrid orbitals (GHO). In addition to the previous ones, we examine a restrained transformation matrix based on the assumption that all coefficients of the p-hybridized orbitals are uniform and each hybridized orbital points toward a vertex of a tetrahedron. It is clearly shown that the new implementation improves the accuracy of the GHO method reducing the error concerning the Pauli repulsion about auxiliary orbitals.

Femtosecond response in rare gas matrices doped with NO impurities: A stochastic approach by G. Rojas-Lorenzo; A.S. Sanz; J. Rubayo-Soneira; S. Miret-Artés (349-353).
Femtosecond dynamics of impurities in solids is analyzed from an alternative theoretical framework to standard molecular dynamics simulations: a stochastic approach.The femtosecond response of NO-doped rare gas matrices is studied within a stochastic Langevin theoretical framework. As is shown, a simple damped harmonic oscillator model can describe properly the absorption and emission line shapes associated with the NO ( A 2 Σ + ↔ X 2 Π ) electronic transitions inside these media as well as the matrix first solvation shell response in a process with two timescales, finding a fairly good agreement with available experimental data. This approach thus constitutes an alternative and complementary way to analyze the structural relaxation dynamics of systems in liquids and solids, leading to a better understanding of the underlying physics.

Kinetic isotope effect on the proton-transfer in indigo carmine by Izumi Iwakura; Atsushi Yabushita; Takayoshi Kobayashi (354-357).
The proton transfer in the indigo carmine after photo-excitation the observed k a H / k a D ratio was 1.5.We have found that photo-excited indigo carmine causes stepwise proton transfer to generate mono-alcohol intermediate, which immediately returns to the parent molecule [I. Iwakura, A. Yabushita, T. Kobayashi, Chem. Lett. 38 (2009) 1020]. The kinetic isotope effect in the proton transfer of this system has been studied by direct observation of the real-time molecular vibrational amplitude during the reaction including the transition state using a sub-5-fs laser pulse. The k a H / k a D ratio for the proton transfer after photo-excitation is observed to be 1.5 ± 0.1.

The time dependence of the survival probabilities for A + B → C reaction in regular and fractal dimensions.Fluctuation-induced kinetics of diffusion-influenced reactions in fractal dimensions have been studied. The fluctuations in concentrations of the reactants dominate the long-time dynamics and efficient numerical methods are needed to quantify the long-time fluctuation effects. We present the generalized numerical methods that are efficient especially for the investigation of the long-time dynamics. Numerical solutions of new coupled diffusion–reaction equations obtained by applying hierarchical Smoluchowski approaches to A + A → C and A + B → C reactions in fractal dimensions show that the present numerical methods produce accurate long-time results efficiently in fractal dimensions.

Relative electrophilicity and aromaticity by Siamak Noorizadeh; Ehsan Shakerzadeh (363-367).
Using Isomerization method and MEP, the relationships are investigated between different methods of electrophilicity calculations and aromaticity.Using the isomerization method, Isomerization Stabilization Energies (ISEs) are computed for some five-membered heterocyclic rings, penta- and hepta-fulvene compounds. Using quadratic model (ΔωQ ), Janak’s approximation (ΔωJ ) and recently introduced Morse-Like function approach (ΔωM ) the relative electrophilicities are evaluated for these systems. An excellent linear correlation between the latter and some aromaticity measures are observed and also the orders of aromaticities are successfully predicted using the Minimum Electrophilicity Principle (MEP). Therefore, it is claimed that for prediction of electrophilicities in different systems, the obtained values from the Morse-Like function are more reliable than those which are calculated from the approximate models.

Alloying effect on K shell X-ray fluorescence parameters and radiative Auger ratios of Co and Zn in Zn x Co1− x alloys by N. Kup Aylikci; E. Tiraşoğlu; İ.H. Karahan; V. Aylikci; E. Cengiz; G. Apaydin (368-373).
In this Letter, charge transfer effect on the K X-ray intensity ratios, production cross-sections, fluorescence yields, KLM/Kα and KMM/Kβ radiative Auger intensity ratio values of Co and Zn elements in various alloys were investigated, respectively.(a) Typical K X-rays spectra of Zn in Zn0.94Co0.06 alloy. (b) A residue spectrum with respect to K X-ray spectra of Zn in Zn0.94Co0.06 alloy.In this study, σKα,β production cross-sections, ωK fluorescence yields, Kβ/Kα, KLM/Kα and KMM/Kβ intensity ratios of Co and Zn in different alloy compositions were measured. The alloying effects on the fluorescence parameters of Co and Zn were investigated. The changes in these parameters were interpreted according to the rearrangement of valance state electrons and the charge transfer process between the 3d elements which constitute the alloys. The samples were excited by 59.5 keV γ-rays from a 241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.

Plane wave cut-off value for a converged description of electronic and structural properties is studied.Periodic systems are best described by the pseudo-potential methods. However, the accuracy of its description depends on the cut-off of plane wave basis. This is much more critical in the case of weak interactions, where a clear understanding on the influence of plane wave cut-off on the structural and electronic properties is not readily available in the literature. In the present work, we have taken a metal substituted beta zeolite–H2O complex for understanding this objective. Our studies show that while a lower cut-off of 500 eV is sufficient for the convergence of the structural parameters, description of energy-dependent properties necessitates a high cut-off value.

FMO-MD, an ab initio molecular dynamics method, was improved by the introduction of 3-body expansion (FMO3) and generalized dynamic fragmentation.The fragment molecular orbital-based molecular dynamics (FMO-MD) was improved by the introduction of the three-body extension (FMO3) and the generalized dynamic fragmentation. An analytical energy gradient was derived for FMO3 to realize FMO3-MD. An algorithm of generalized dynamic fragmentation was devised to treat each covalent-bonded and, optionally, hydrogen-bonded atom cluster as a fragment in the course of FMO-MD. The new algorithms were tested by performing conventional MO-MD, FMO2-MD, based on two-body extension, and FMO3-MD simulations of (H2O)32 and H+(H2O)32. FMO2-MD resulted in lower precision, especially in H+(H2O)32, while FMO3-MD gave a precision comparable to that of MO-MD.

Being independent of the sign of parameter b 2 0 , it is close gradually to zero point along with parameter R increasing.Using the unified ligand-field coupling scheme, the local structures and optical spectra of octahedral Fe3+ centers in a series of garnet crystals have been investigated systematically with two different values of parameter A 4. Our results show that the local structures of octahedral Fe3+ centers in doped systems are similar to one another if there are the same external environments around B ions in the host crystals. Being independent of the sign of the spin Hamiltonian parameter b 2 0 , it is increasingly close to zero along with structure parameter R increasing. Moreover, b 2 0 is almost linear with the change of structure parameter θ.

A strategy for obtaining a more accurate transition state estimate using the growing string method by Anthony Goodrow; Alexis T. Bell; Martin Head-Gordon (392-398).
Total CPU time for determining the final transition state, comprised of the time for determining the initial Hessian and the time for performing the transition state optimization. A summary of the results from three different reactions are shown, which highlight the effectiveness of estimating the transition state through interpolation during the reparameterization step of the modified-growing string method.The present study describes a new method for obtaining a more accurate transition state estimate through interpolation of the reaction pathway. The method can be implemented using the reaction pathway or during the reparameterization step of the modified-growing string method. The transition state estimate is obtained by mapping the location of the maximum in energy along the reaction pathway to a set of coordinates in phase space. This method has been tested on three reactions of increasing complexity, representing a 35.0–77.8% reduction in CPU time for the transition state optimization calculation compared to using the geometry highest in energy.

Linearization approximations and Liouville quantum–classical dynamics by Sara Bonella; Giovanni Ciccotti; Raymond Kapral (399-404).
Equivalence of the mixed quantum–classical Liouville dynamics and the linearization methods for the propagation of the density operator is shown.We show that linearization methods, commonly used to approximate the evolution of the density operator in mixed quantum–classical systems, can be justified when a small parameter, the ratio of masses of the quantum subsystem and bath, is introduced. The same parameter enters in the derivation of the quantum–classical Liouville equation. Although its original derivation followed from a different formalism, here we show that the basis-free form of the quantum–classical Liouville equation for the density operator can also be obtained by linearization of the exact time evolution of this operator. These results show the equivalence among various quantum–classical schemes.

Author Index (405-411).