Chemical Physics Letters (v.412, #4-6)
Editorial Board (CO2).
Accurate vibrational frequencies using the self-consistent-charge density-functional tight-binding method by Edyta Małolepsza; Henryk A. Witek; Keiji Morokuma (237-243).
An optimization technique for enhancing the quality of repulsive two-body potentials of the self-consistent-charge density-functional tight-binding (SCC-DFTB) method is presented and tested. The new, optimized potentials allow for significant improvement of calculated harmonic vibrational frequencies. Mean absolute deviation from experiment computed for a group of 14 hydrocarbons is reduced from 59.0 to 33.2 cm−1 and maximal absolute deviation, from 436.2 to 140.4 cm−1. A drawback of the new family of potentials is a lower quality of reproduced geometrical and energetic parameters.
Analytical expressions of exchange and three-center nuclear attraction integrals over 1s and 2s Slater orbitals with different exponents by María Belén Ruiz; Katrin Peuker (244-249).
Compact analytical formulas are given for exchange integrals and three-center nuclear attraction integrals using nonorthogonal Slater orbitals with equal and different exponents which appear in a Hylleraas-CI basis. Since all exponents in the integrals may be different, they are appropriate to optimize exponents and therefore to shorten the wave function expansions.
Wetting of doped carbon nanotubes by water droplets by E.M. Kotsalis; E. Demosthenous; J.H. Walther; S.C. Kassinos; P. Koumoutsakos (250-254).
We study the wetting of doped single- and multi-walled carbon nanotubes by water droplets using molecular dynamics simulations. Chemisorbed hydrogen is considered as a model of surface impurities. We study systems with varying densities of surface impurities and we observe increased wetting, as compared to the pristine nanotube case, attributed to the surface dipole moment that changes the orientation of the interfacial water.We demonstrate that the nature of the impurity is important as here hydrogen induces the formation of an extended hydrogen bond network between the water molecules and the doping sites leading to enhanced wetting.
Binding and relaxation behavior of Coumarin-153 in lecithin–taurocholate mixed micelles: A time resolved fluorescence spectroscopic study by Debdeep Chakrabarty; Anjan Chakraborty; Debabrata Seth; Partha Hazra; Nilmoni Sarkar (255-262).
The microenvironment of the bile salt–lecithin mixed aggregates has been investigated using steady state and picosecond time resolved fluorescence spectroscopy. The steady state spectra show that the polarity of the bile salt is higher compared to lecithin vesicles or the mixed aggregates. We have observed slow solvent relaxation in bile salt micelles and lecithin vesicles. The solvation time is gradually slowed down due to gradual addition of the bile salt in lecithin vesicles. Addition of bile salt leads to the tighter head group packing in lecithin. Thus, mobility of the water molecules becomes slower and consequently the solvation time is also retarded. We have observed bimodal slow rotational relaxation time in all these systems.
High-aperture-excitation and -detection fluorescence spectroscopy with polarized light by J.J. Fisz; M. Buczkowski; P. Żuchowski (263-268).
A description of fluorescence depolarization spectroscopy in the case of high-aperture-detection and -excitation is considered and described in spherical representation. The formalism outlined applies to one- and two-photon-excitation polarized fluorescence spectroscopy for different kinds of molecular media, including thin layers of organized molecular assemblies, solutions and interfaces. It applies to standard fluorescence and time-resolved linear dichroism measurements, fluorescence microscopy and evanescent-wave-excitation fluorescence experiments.
Growth, nitrogen doping and characterization of isolated single-wall carbon nanotubes using liquid precursors by Gayatri Keskar; Rahul Rao; Jian Luo; Joan Hudson; Jia Chen; Apparao M. Rao (269-273).
Isolated single wall carbon nanotubes (SWNTs) were prepared on bare quartz and SiO2/Si substrates using a chemical vapor deposition process in which xylene was used as the carbon source. Controlled doping of isolated SWNTs with nitrogen was achieved by mixing appropriate amounts of acetonitrile with xylene. As the nitrogen concentration in the feed was increased from 0 to 33 at.%, the radial breathing mode intensity decreased dramatically while the intensity of the D-band increased gradually relative to that of the G-band. The D′-band at ∼1620 cm−1 was observed in the Raman spectrum when the nitrogen concentration reached ∼2–3 at.%.
Hyper-Rayleigh scattering of neutral and charged helicenes by Edith Botek; Milena Spassova; Benoît Champagne; Inge Asselberghs; André Persoons; Koen Clays (274-279).
Oxidation effects on the hyper-Rayleigh scattering (HRS) second-order nonlinear optical responses of homo- and hetero-helicenes have been investigated using the time-dependent Hartree–Fock approach and the Austin Model 1 semi-empirical Hamiltonian. Upon oxidation, this approach predicts a substantial increase of the HRS response, which, with the exception of tetrathia--helicene and pentathia--helicene, is accompanied by a decrease of the depolarization ratio. In the case of helicenes bearing thiophene units, the HRS increase is associated with the presence of a substantial axial contribution to the first hyperpolarizability, whereas the radial component is otherwise dominant.
Replica-exchange molecular dynamics simulation of small peptide in water and in ethanol by Koji Yoshida; Toshio Yamaguchi; Yuko Okamoto (280-284).
Replica-exchange molecular dynamics simulations have been performed on a 10-residue peptide in ethanol as well as in water that were treated explicitly with 32 replicas in the range of 298–600 K. It has been found that the peptide tends to form compact structures in ethanol whereas it is extended in water. The numbers of intramolecular hydrogen bonds and turn structures are both larger in ethanol than in water, and this difference enhances the tendency of forming secondary structures in ethanol.
MP2 and DFT studies of the DNA rare base pairs: The molecular mechanism of the spontaneous substitution mutations conditioned by tautomerism of bases by Victor I. Danilov; Victor M. Anisimov; Noriyuki Kurita; Dmytro Hovorun (285-293).
We investigated structures and electronic properties of DNA base pairs containing the lactim forms of guanine (G*) or thymine (T*) as well as the imino forms of cytosine (C*) or adenine (A*) by ab initio MP2 and DFT methods. The found stable structures of G*–T and G–T* base pairs are the nonplanar ones. The obtained formation energies indicate that G*–T and A–C* are more favorable than G–T* and A*–C. The nature of their hydrogen bonding was discussed based on the energy decomposition analysis of Morokuma–Kitaura and the reduced-variational-space methods to elucidate the possibility of the tautomerization of DNA base pairs.
Fabrication of organic copper phthalocyanine nanowire arrays via a simple AAO template-based electrophoretic deposition by Hua-Bing Xu; Hong-Zheng Chen; Wen-Jun Xu; Mang Wang (294-298).
Copper phthalocyanine (CuPc) nanowire arrays were fabricated for the first time by the electrophoretic deposition (EPD) method using a porous anodic aluminum oxide (AAO) template. The barrier layer between the aluminum substrate and the AAO membrane was first removed by progressively reducing the applied anodizing voltage. The AAO template was then employed directly to fabricate CuPc nanowire arrays by direct current EPD. The morphology of the CuPc nanowires was characterized by transmission electronic microscopy and field emission scanning electronic microscopy. The nanowires exhibited smooth surfaces and uniform diameters of about 40 nm. The photoconductivity of the CuPc nanowire arrays was investigated as well.
Structure and stability of perazido substituted azacycloalkanes, N n (N3) n by Hai-Shun Wu; Xiao-Hong Xu; Haijun Jiao (299-302).
The structure and stability of azido azacycloalkanes, N n (N3) n (n = 3–6), have been investigated at the B3LYP/cc-pvTZ level of density functional theory. The stability obeys the gauche effect. The most stable structure is N5(N3)5 (7), while N3(N3)3 (2) is the least stable structure. They are thermodynamically unstable towards dissociation into N2.
Length and temperature dependence of electrical conduction through dithiolated porphyrin arrays by Bong Keun Kang; Naoki Aratani; Jong Kuk Lim; Dongho Kim; Atsuhiro Osuka; Kyung-Hwa Yoo (303-306).
We present an investigation of electrical transport through fused and orthogonal dithiolated porphyrin arrays of different molecular lengths. Length dependence measurements show that conductance decreases much more slowly with molecular length than the exponential dependence expected for a coherent tunneling process. It suggests that the electrical conduction through porphyrin arrays is mainly due to the thermally activated hopping transport. From the temperature dependence of I SD–V SD curves, the thermal activation energy E a is estimated to be about 0.35 eV at zero-bias voltage, independently of molecular conformation and length.
Dynamic folding pathway models of α-helix and β-hairpin structures by In-Ho Lee; Seung-Yeon Kim; Jooyoung Lee (307-312).
We present dynamic folding pathway models of α-helix and β-hairpin structures at atomistic details by using the action-derived molecular dynamics method. The present formulation is free from common assumptions widely used in molecular dynamics such as high temperature simulations, a choice of order parameter set, an arbitrary identification of the folded configuration, or an exponential kinetics. The present dynamic folding pathway models for both helix and hairpin formations are consistent with experimental data.
Luminescence of (Li0.333Na0.334K0.333)Eu(MoO4)2 and its application in near UV InGaN-based light-emitting diode by Zhengliang Wang; Hongbin Liang; Liya Zhou; Hao Wu; Menglian Gong; Qiang Su (313-316).
A novel red phosphor, (Li0.333Na0.334K0.333)Eu(MoO4)2 (LNKEM), was prepared by solid state reaction technique at high temperature. Its photo-luminescent property was investigated and compared with that of Y2O2S: 0.05Eu3+, the phosphor currently used in near UV LED (light-emitting diode). It is found that LNKEM shows higher luminescent intensity, and the CIE (Commission Internationale de l’Eclairage, International Commission on Illumination) chromaticity coordinates of LNKEM is closer to the NTSC standard values than that of Y2O2S: 0.05Eu3+. An intense red-emitting LED was fabricated by combining mono-phosphor LNKEM with a ∼400 nm emitting InGaN chip.
A direct ab initio dynamics study of the initial decomposition steps of gas phase 1,3,3-trinitroazetidine by Qinghua Zhao; Shaowen Zhang; Qian Shu Li (317-321).
The dynamics of initial decomposition of gas phase 1,3,3-trinitroazetidine (TNAZ) is investigated by using B3LYP/6-31+G(d,p) method and microcanonical variational transition state theory. Three initial decomposition pathways, NO2 fission, HONO elimination, and direct ring-opening reaction are considered. The calculated rate constants indicate that the rate constants of NO2 fission reaction are larger than those of both HONO elimination and ring-opening reaction in gas phase. However, HONO elimination and ring-opening channels may be important for the decomposition reaction of TNAZ in solid state. These results provide new understanding of the dynamics of the initial decomposition steps of TNAZ.
Investigation of moisture diffusion in epoxy system: Experiments and molecular dynamics simulations by Y.C. Lin; Xu Chen (322-326).
Epoxy resins are attractive materials for many engineering applications. However, they are susceptible to the moisture environment and can be degraded by the moisture. The moisture diffusion characterizations, which include weight changes, diffusion coefficients and the activation energy, have been investigated. The experimental results show that the desorption process from highly moisture-saturation tended to leave a small residual moisture content, which could only be removed by heating at relative high temperature. The further interpretation of this phenomenon is given from the activation of bound waters, by experiments and molecular dynamics simulations.
Electron momentum distribution mapping of trans-stilbene single crystal by positron annihilation by Krishnan Sivaji; Arjunan Arulchakkaravarthi; Sellaiyan Selvakumar; Perumalsamy Ramasamy; Sambasivam Sankar; Babu Varghese (327-330).
Two-dimensional electron momentum distributions mapping in a molecular trans-stilbene crystal has been done, first time using two-dimensional angular correlation of positron annihilation radiation. The measured coincident annihilation spectra for the plane corresponding to c–a, projected to crystallographic b direction have been elucidated.
Improvement in performance of organic light-emitting diodes by adjusting charge-carrier mobility in organic/inorganic hybrid hole transporting layer by Fushan Li; Zhijian Chen; Chunling Liu; Qihuang Gong (331-335).
The charge-carrier transportation in an organic/inorganic (triphenylamine/SiO2) hybrid film was studied using time-of-flight photocurrent measurement. The hole-mobility increases with triphenylamine concentration and hole transportation in this film corresponds to hopping model. The organic light-emitting diodes (OLEDs) based the organic/inorganic hybrid film as hole-transporting layer were fabricated and electroluminescent characteristics were investigated. The experiments demonstrated that emitting efficiency reached a max value by varying triphenylamine content. A simple model is proposed to explain this character and the theoretical analysis is consistent with the experimental results.
Bipartivity of fullerene graphs and fullerene stability by Tomislav Došlić (336-340).
A recently introduced measure of bipartivity in complex networks is tested in the role of a selector of stable fullerene isomers. Its performance is compared with other proposed stability predictors on the set of experimentally characterized fullerene isomers. It is found out that the new predictor exhibits a high degree of selectivity. This, together with the simplicity of its implementation and low computational complexity, makes it a useful tool in narrowing the set of candidates for stable fullerene isomers.
Radiative decay engineering by triaxial nanoellipsoids by D.V. Guzatov; V.V. Klimov (341-346).
Radiative decay rate of an atom placed near a triaxial nanoellipsoid is investigated. Analytical results are obtained for a general case. It is shown that a triaxial ellipsoid can be used for an efficient control of the decay rate of an atom, molecule or quantum dot and for high-efficiency coupling of the far field radiation to the near-field domain. For example, the decay rate near a silver ellipsoid can be enhanced by five orders of magnitude. It is also shown, that a triaxial nanoellipsoid can be used for simultaneous efficient control of absorption and emission rates of fluorophores.
H atom-induced oxidation reaction on water-terminated Si surface, 2H + H2O/Si(1 0 0)–(2 × 1): A theoretical study by Hidekazu Watanabe; Zhi-Hong Wang; Shinkoh Nanbu; Jun Maki; Tsuneo Urisu; Mutsumi Aoyagi; Kenta Ooi (347-352).
The reported oxidation reaction observed by BML-IRRAS spectra on the silicon surface system, 2H + H2O/Si(1 0 0), has been studied by an ab initio molecular orbital method. The highest transition state is found at ≈+25 kJ/mol from the reactant energy level, and the oxidation occurs easily under the experimental condition. The present study also accounts for the reactivity deduced from the absorption bands in the IR spectra. It is noted that the quenching of the reaction by thermal relaxation is impossible because the surface is not trapped into the metastable states located much lower in energy than the reactant.
Applications of genetic algorithms for inverting positron lifetime spectrum by N.H.T. Lemes; J.P. Braga; J.C. Belchior (353-358).
Inversion of positron lifetime spectrum is performed via genetic algorithms considering a simulating counting of positron annihilation. Preliminary analysis without the inclusion of noise and for only one run produced large oscillations for the second peak in the inverted spectrum. An alternative strategy was proposed to reduce the oscillations that produced an average error of 0.03%. A maximum error of 40% was considered in the simulated data that produced a random average error of 10% in the counting data. The final inverted spectrum considering this error is in reasonable agreement with the exact result, producing a relative error of 2%.
Structure and vibrational spectra of dimethylsilanediol and methylsilanetriol dimers by I.S. Ignatyev; M. Montejo; F. Partal Ureña; J.J. López González (359-364).
Equilibrium geometries of methylsilanetriol monomer and dimers are obtained at B3LYP/DZP + diff level and differences in electron density distribution and in hydrogen bonding between them and analogous structures of dimethylsilanediol are discussed. Five isomers are found as energy minima in the [CH3Si(OH)3]2 system, from which the most stable corresponds to a structure in which all three OH groups of the monomers are involved in hydrogen bonding. The predicted vibrational spectra of dimethylsilanediol and methylsilanetriol dimers reveal the considerable decrease of νOH and increase of δSiOH frequencies in silanetriol dimers.
Ab initio studies of the dipole moment and polarizability of azulene in its ground and excited singlet states by Alan Hinchliffe; Humberto J Soscún (365-368).
We report ab initio energies, dipole moments and dipole polarizabilities for the ground and five lowest electronic excited singlet states of azulene. Ground state properties were calculated using the HF and B3LYP models, whilst excited states were modelled using CIS and CIS(D). Our dipole moment polarity agrees with experiment, but the numerical agreement is qualitative. The ground state dipole polarizabilities agree with experiment and with other theoretical studies. The excited state polarizabilities are consistent with the sparse experimental data and we predict immensely enhanced dipole polarizabilities for the higher excited states.
Enhancement of hydrogen storage capacity of carbon nanotubes via spill-over from vanadium and palladium nanoparticles by Renju Zacharia; Keun Young Kim; A.K.M. Fazle Kibria; Kee Suk Nahm (369-375).
The hydrogen storage capacities of palladium- and vanadium-doped carbon nanotubes (CNTs) at room temperature were investigated using the Sieverts apparatus. The storage capacity of Pd- and V-doped CNTs at 2 MPa were found to be 0.66 and 0.69 wt%, which are nearly 30% more than that of the pristine-CNTs. Also, the doped-CNTs exhibited faster initial hydrogen adsorption kinetics when compared with the pristine samples. The compensation of hydrogen storage by the metal particles in the doped-CNTs reveals that metal particles enhance the storage capacity via the spill-over mechanism. The re-adsorption studies of previously adsorbed samples suggested that nearly 70–85% of the spilled hydrogen occupies the physisorption binding sites, such as external-walls or groove-sites of CNTs.
A new search algorithm for QSPR/QSAR theories: Normal boiling points of some organic molecules by Pablo R. Duchowicz; Eduardo A. Castro; Francisco M. Fernández; Maykel P. Gonzalez (376-380).
We test a new algorithm for the search of an optimal subset of molecular descriptors from a large set of them. As a practical realistic application we predict the normal boiling points of 200 organic molecules by means of molecular descriptors selected from a set of more than thousand of rigid molecular descriptors produced by the DRAGON 5 evaluation software, plus two flexible descriptors. We thus improve previous results derived from the application of Correlation Weighting of Atomic Orbitals with Extended Connectivity of Zero- and First-Order Graphs of Atomic Orbitals.
Extracular densities of the non-Born–Oppenheimer Hookean H2 molecule by Xabier Lopez; Jesus M. Ugalde; Eduardo V. Ludeña (381-385).
The exact nuclear and electronic extracular non-Born–Oppenheimer density functions and their associated probability functions have been obtained for the spherical ground and excited states of the Hookean hydrogen molecule. The salient features of these complex nodal functions are discussed aided by their mean expectation values and fluctuations. The infinite nuclear mass limit is shown to appear naturally from the derived equations.
Molecular rotation–vibration coupling by quantum wavepacket interference at potential energy curve crossings by Niklas Gador; Bo Zhang; Tony Hansson (386-390).
Quantum wavepacket interference is shown to result in modulation of the ultrafast transient anisotropy of a diatomic molecule. The molecule is in a state comprising two bound electronic states at intermediate coupling strength and the anisotropy modulation enters via variations in the instantaneous contributions of the initial states to the total anisotropy. A necessary condition for the appearance of the modulation is that the involved rotational states possess different vibrational dynamics. The wavepacket interference mediates this coupling by imposing dynamical restrictions on the accessible vibrational phase space which depend on the rotational state.
Blueshift of the photoluminescence excitation band of the Sm3+ impurity in Pt–CeO2 powder induced by the electron transfer between CeO2 and Pt particles by Hiromitsu Nakajima; Toshiyuki Mori (391-394).
The photoluminescence (PL) and PL excitation spectra of pure and Pt-loaded CeO2 powders were measured, and the PL peaks from the Sm3+ impurity were observed. We found that, as the Pt concentration increases, the peak intensity decreases and the PL excitation band blueshifts. These relationships can be explained by considering electron transfer and difference in work function between CeO2 and Pt. Moreover, we found a quantitative relationship between the blueshift and the difference in work function. These results suggest that the degree of contact and extent of electron transfer between CeO2 and Pt can be estimated from PL spectroscopy.
Raman spectral changes of PEDOT–PSS in polymer light-emitting diodes upon operation by Satoshi Sakamoto; Masanori Okumura; Zinggang Zhao; Yukio Furukawa (395-398).
The micro-Raman spectra of a double-layer light-emitting diode fabricated with poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT–PSS) as a hole-injection layer and poly(2,7-(9,9-dioctylfluorene)-alt-benzothiadiazole) (F8BT) blended with poly(9,9-dioctylfluorene) (PF8) as an emissive layer have been measured with excitation at 633 nm. After the operation of the device, the intensities of the bands due to PEDOT have increased. These increases in Raman intensity have been attributed to the reduction (dedoping) of PEDOT chains during operation on the basis of the results of electrochemical oxidation and reduction of a PEDOT–PSS film. The reduction of PEDOT chains is most likely one of the intrinsic factors of the degradation of polymer light-emitting diodes.
Extinction and orientational dependence of electron diffraction from single-walled carbon nanotubes by Zejian Liu; Lu-Chang Qin (399-405).
The extinction and orientational dependence of electron diffraction from single-walled carbon nanotubes have been observed experimentally and investigated in detail theoretically using both algebraic analysis and numerical simulations. Electron diffraction from only achiral carbon nanotubes of zigzag or armchair structure shows observable orientational dependence and extinction of certain layer lines in experiment due to the interference of two primary Bessel functions of the same order that contribute to the scattering intensities on these layer lines.
Quantum chemical study of coherent electron transport in oligophenylene molecular junctions of different lengths by Wenyong Su; Jun Jiang; Yi Luo (406-410).
The coherent electron transportation properties of the gold–oligophenylene–gold junctions of different lengths have been studied by means of a generalized quantum chemical approach. The experimentally measured length dependence of current flow in the junctions has been well reproduced by the hybrid density functional theory calculations. It is found that the current–voltage characteristics of the junctions depend strongly on the metal–molecule bonding distances. With the help of the calculations, the possible gold–molecule bonding distances in the experimental devices are identified.
The magneto-optical properties of diastereoisomers by Thierry Ruchon; Jean-Yves Thépot; Marc Vallet; Albert Le Floch (411-415).
Enantiomers exhibit opposite optical activities but identical Faraday rotations. We demonstrated that the corresponding meso molecules, whose optical activities vanished because of an internal compensation, exhibited Faraday rotations different from their chiral diastereoisomers. In the case of tartaric acid, the excess of Faraday rotation compared to a water-filled reference cell, and measured using a differential method, was two times greater for the meso than for the chiral isomers. This result was in agreement with a theoretical model based on the dipole–dipole interaction model, which took into account the applied magnetic field.
The binding of the noble metal cations Au+ and Ag+ to propene by Ryan Olson; Sergey Varganov; Mark S. Gordon; Horia Metiu (416-419).
The binding energies for the reaction M+ + CH2 ＝CHCH3 → M+[CH2 ＝CHCH3], for M = Ag, Au, are predicted using both second order perturbation theory (MP2) and coupled cluster theory (CCSD(T)). Systematically improving the quality of the atomic basis set to the complete basis set limit produces a monotonic improvement in the predicted binding energy for M = Ag relative to the experimentally determined value; the final predicted binding energy is within experimental error. Conversely, the same systematic improvement in the atomic basis set results in successively worse agreement at the MP2 level of theory.
Investigation of microwave effects on the oscillatory Bray–Liebhafsky reaction by Dragomir R. Stanisavljev; Antonije R. Djordjević; Vladana D. Likar-Smiljanić (420-424).
A specific control of the Bray–Liebhafsky oscillatory reaction is achieved by changing the microwave (MW) participation in heating the reaction mixture. Experiments are performed at temperatures T rm = 62, 65, 68 °C. Before the bifurcation point, increased MW participation has no effect on the reaction mechanism. In the sensitive state close to the bifurcation point, increased MW participation stops the oscillatory evolution. To explain the reaction dynamics in the MW field, we consider classical causes (overheating and convection effects) in contrast to some specific effects of the MW heating.
Intermolecular charge and energy transfer in neurosporene and chlorophyll a derivative complex by Mengtao Sun; Yuanzuo Li; Fengcai Ma (425-429).
Dye-sensitized solar cells using a chlorophyll a derivative (PPB a der.) as the sensitizer and carotenoids having different conjugation lengths as redox spacers was studied experimentally. In this Letter, the excited state properties of the neurosporene & PPB a der. complex are investigated theoretically with quantum chemistry method. The 2D real space analysis with the transition density matrix reveals that some excited states are locally excited states, and some is the intermolecular charge transfer (ICT) state. The 3D real space analysis reveals: (1) that the orientation and the strength of the dipole moment from transition density, and (2) the orientation and result of ICT in Neurosporene & PPB a der. complex from charge difference density.
Improved multi-level electronic structure methods (MLSEn + d) for atomization energies and reaction energy barriers by Tsung-Hui Li; Hui-Ru Chen; Wei-Ping Hu (430-433).
We have improved our multi-level electronic structure methods MLSEn for calculating the atomization energies and reaction energy barriers for neutral systems by using improved correlation-consistent basis sets for second-row elements. The re-parameterization of the improved methods MLSEn + d was based on updated databases of 109 atomization energies, 38 hydrogen-transfer barrier heights, and 22 neutral reaction barrier heights from a recently developed database of non-hydrogen-transfer reactions. The improved methods perform very well on all three types of energies with mean unsigned errors of 0.70, 0.87, and 0.69 kcal/mol by the MLSE4 + d method.
Methylsilane on Cu(1 1 1): A MDS study of the formation of the surface silicide by Hervé Ménard; Andrew Pratt; Marcus Jacka (434-438).
The adsorption of methylsilane on Cu(1 1 1) has been investigated by metastable deexcitation spectroscopy. The deexcitation process for the clean copper and silicide surfaces was demonstrated to occur via resonance ionization followed by Auger neutralization, while upon the adsorption of methylsilane at 295 K it changes to Auger deexcitation. Accompanied by ultraviolet photoelectron spectroscopy, the MD spectrum at 295 K reveals the presence of a methyl group on the surface, supporting the assertion that the majority of the surface is covered with methylsilane fragments. Annealing the surface above 420 K reveals the presence of clean copper sites on a partially silicide surface.
The interaction of N2 with active sites of a single-wall carbon nanotube by Yi-Jun Xu; Jun-Qian Li (439-443).
The adsorption of N2 at the edge of a single-wall carbon nanotube (SWNT) has been investigated employing an ONIOM approach. It was found that N2 can be chemisorbed at the edge site of zigzag SWNT surface and the N–N bond is activated. However, the adsorption at the edge site of armchair SWNT surface is rather weak. This can be attributed to the crucial effect of local edge carbon atoms arrangement of the defect SWNT surface with open tips. Furthermore, our results strongly reinforce the viewpoint from recent experimental observations and theoretical studies that SWNTs with open tips exhibit larger adsorption capacity than closed-ended SWNTs.
Anode catalysts for enhanced methanol oxidation: An in situ XANES study of PtRu/C and PtMo/C catalysts by S. Mylswamy; C.Y. Wang; R.S. Liu; J.-F. Lee; M.-J. Tang; J.-J. Lee; B.-J. Weng (444-448).
Pt/C, PtRu/C and PtMo/C electro catalysts were prepared in different compositions by incipient wetness impregnation method. These catalysts were characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) to understand the miscibility into solid solution and to calculate the d-orbital vacancy, respectively. Pt with Ru and Mo forms a single alloy which was confirmed by XRD date. XANES was measured at Pt LII and LIII edges and K edges of Ru and Mo to determine the oxidation states of these metals in different compositions. Further calculations of d-orbital vacancy of Pt revealed more information that increasing the Ru or Mo content increases d-orbital vacancy. As Mo oxidizes faster than Ru, magnitude of d-orbital vacancy is high in the case of Ru compared to Mo. In situ XENES study was also conducted in methanol fuel cell to understand the oxidation states and methanol oxidation mechanism.
Raman scattering analysis of changes induced by chemical treatment of double-walled carbon nanotubes by Amanda V. Ellis; Andrea Bubendorfer (449-453).
Here we examine the changes in double-walled carbon nanotubes with two chemical treatments using Raman scattering spectroscopy at an excitation of 632.8 nm (1.96 eV). The nanotubes were acid treated then subsequently treated with phosphorus pentasulfide (a mild electrophillic catalyst). While the treatment process maintains the integrity the nanotubes, Raman analysis indicates the outer shells loose their electron–phonon resonance and metallic character, leaving only the tangential mode from the secondary (inner) tubes. After chemical treatment the strongly up-shifted G-band, at 1585 cm−1, has been designated as secondary semiconductor tubes, exhibiting resonant scattering via E 22 s
Indium-related novel architecture of GaN nanorod grown by molecular beam epitaxy by Young Heon Kim; Jeong Yong Lee; Seong-Ho Lee; Jae-Eung Oh; Ho Seong Lee; Yoon Huh (454-458).
Gallium nitride nanorods with indium-related novel architecture have been grown on silicon (1 1 1) substrate by molecular beam epitaxy. Indium was supplied during the growth to synthesize the ternary InGaN. Scanning electron microscope images indicate that the nanorods have several short branches. Energy dispersive X-ray spectroscopy reveals that the indium was included at the specified-region of the nanorod and the branches are pure GaN. The branches grow on the InGaN segment. Cathodoluminescence spectrum of the nanorods shows two peaks at room temperature, which are around 3.10 and 3.40 eV, respectively.
Site-specific fragmentation caused by Si:1s core-level photoionization of F3SiCH2CH2Si(CH3)3 vapor by S. Nagaoka; Y. Tamenori; M. Hino; T. Kakiuchi; J. Ohshita; K. Okada; T. Ibuki; I.H. Suzuki (459-463).
Ionic fragmentation caused by Si:1s photoionization of 1-trifluorosilyl-2-trimethylsilylethane [F3SiCH2CH2Si(CH3)3] vapor was studied by the energy-selected photoelectron photoion coincidence method and monochromatized synchrotron radiation. In the 1s photoionization at the Si atom bonded to three F atoms, H+ exceeded the other ions in the peak height, and production of SiF 3 + ion seemed to be reduced. On the other hand, the 1s photoionization at the other Si atom bonded to three CH3 groups enhanced production of H+ ion with high kinetic energy. These results suggest that Si:1s photoionization causes site-specific fragmentation.
Solvent-dependent intra- and intermolecular vibrational energy transfer of W(CO)6 probed with sub-picosecond time-resolved infrared spectroscopy by Motohiro Banno; Shin Sato; Koichi Iwata; Hiro-o Hamaguchi (464-469).
Solvent-dependent intra- and intermolecular vibrational energy transfer from the triply degenerate CO stretch mode of W(CO)6 is observed in nine alkanes (C n H2n + 2, n = 5–13) with single-color sub-picosecond time-resolved infrared spectroscopy. In all the solvents, the vibrational relaxation process is well characterized by three time constants: τ 1 (<1 ps), τ 2 (3–13 ps) and τ 3 (124–160 ps). The solvent dependence of τ 2 and τ 3 cannot be explained by the macroscopic properties of the solvent. In particular, the longest time constant τ 3 shows the minimum value of 124 ps in decane among the nine alkanes. The rate of the vibrational energy relaxation is a sensitive measure of the microscopic environments.
Multifrequency EPR study and DFT calculations of a C60 bisadduct anion by Alfonso Zoleo; Marco Bellinazzi; Maurizio Prato; Marina Brustolon; Anna Lisa Maniero (470-476).
The monoanion of bis-TRANS2-[N-methyl-3,4-fulleropyrrolidine] (TRANS2−) was investigated by continuous wave (CW) and pulsed EPR. X-band spectra showed signals due to 14N and 13C hyperfine couplings (hcc). DFT calculations of 14N and 13C isotropic hcc were performed on TRANS2− for different conformations of the pyrrolidinic rings. Calculated values, averaged over the conformations, match well with the experimental values. Accurate g-tensor principal values were obtained by high frequency EPR. The possible dynamical processes affecting the electron spin relaxation are discussed to explain the temperature dependence of the EPR line widths and of the T 2 and T 1 relaxation times obtained by pulsed methods.
Theoretical study of the interaction d10–s2 between Pt(0) and Tl(I) on the [Pt(PH3)3Tl]+ complex by Fernando Mendizabal; Gerald Zapata-Torres; Claudio Olea-Azar (477-481).
We studied the attraction between [Pt(PH3)3] and Tl(I) in the [Pt(PH3)3]–Tl+ complex using ab initio methodology. We found that the changes around the equilibrium distance Pt–Tl and in the interaction energies are sensitive to the electron correlation potential. This effect was evaluated using several levels of theory, including HF, MPn (n = 2–4), CCSD and CCSD(T). The obtained interaction energies differences at the equilibrium distance R e (Pt–Tl) range from 134 to 205 kJ/mol at the different levels used. At long-distances, the behaviour of the [Pt(PH3)3]–Tl+ interaction may be related mainly to charge-induced dipole and dispersion terms, both involving the individual properties of [Pt(PH3)3] and thallium ion. However, the charge-induced dipole term (R −4) is found as the principal contribution in the stability at the long and short distances. The dispersion interaction is smaller, but not negligible near equilibrium distance.
The CO–H interaction on Pt(1 1 1) studied using temperature programmed vibrational sum frequency generation by W.G. Roeterdink; M. Bonn; R.A. Olsen (482-487).
We have studied the interaction between CO and H on Pt(1 1 1) employing Temperature Programmed Vibrational Sum Frequency Generation. Pre-coverage of the Pt(111) crystal with hydrogen redshifts the atop CO stretch vibration by 7–8 cm−1. Below 180 K an inhomogeneous broadening of the CO stretch vibration is observed. Both effects are attributed to hydrogen induced lateral displacement of atop CO. The inhomogeneous broadening is lifted in a thermally activated process, accompanied with a blueshift of the CO stretch vibration of ∼1 cm−1. Corroborated by DFT calculations we suggest that the latter is due to a small tilt of the CO molecule towards the H atom.
Accurate interaction energies for argon, krypton, and benzene dimers from perturbation theory based on the Kohn–Sham model by Rafał Podeszwa; Krzysztof Szalewicz (488-493).
The density-functional-based symmetry-adapted perturbation theory [SAPT(DFT)] has been applied to the argon, krypton, and benzene dimers. It is shown that – at a small fraction of computational costs – SAPT(DFT) can provide similar accuracies for the interaction energies as high-level wave-function based methods with extrapolations to the complete basis set limits. This accuracy is significantly higher than that of any other DFT or DFT-based approaches proposed to date.
Author Index (494-502).