Chemical Physics Letters (v.381, #5-6)
Editorial board (IFC).
Optical activity effect in crystalline structures of purified single-wall carbon nanotubes by A.V Krestinin; A.V Raevskii; N.A Kiselev; G.I Zvereva; O.N Zhigalina; O.I Kolesova (529-534).
Mats and ribbons of well-purified single-wall carbon nanotubes have pronounced optical activity. The effect has been explained by formation of a crystalline structure of the material which was confirmed by high resolution electron microscopy and electron diffraction. Carbon microtubes also have optical activity effect caused by reflection of the light from the smooth wall of the tube close to the Brewster angle.
Overtones of the C–H stretch vibrations on C(0 0 1)(2 ×1 )–H by H. Okuyama; S. Thachepan; T. Aruga; T. Ando; M. Nishijima (535-540).
The overtones of the C–H stretch vibrations on the diamond C(0 0 1)(2 × 1)–H surface are studied by means of electron energy loss spectroscopy (EELS). The dimer structure of the C–H bonds gives rise to the intra-dimer coupling of the C–H stretch vibrations. The fundamental excitations appear at 360 and 362 meV and are assigned to the antisymmetric and symmetric stretch modes, respectively. The overtone excitations are observed at 705 and 1036 meV with two and three quanta on the dimer, respectively. They are analyzed with a model of coupled anharmonic oscillators, and it is shown that the overtone excitations are almost localized on the single C–H bonds.
One-step route to iron oxide-filled carbon nanotubes and bucky-onions based on the pyrolysis of organometallic precursors by Mariane C. Schnitzler; Marcela M. Oliveira; Daniel Ugarte; Aldo J.G. Zarbin (541-548).
Iron and iron oxide-filled carbon nanotubes (CNT) have been produced by an one-step route based on the pyrolysis of ferrocene or a ferrocene-Fe3(CO)12 mixture in a poor oxygen-containing atmosphere, using the reactor quartz tube wall and porous Vycor glass (PVG) as substrate. XRD, TEM and HRTEM studies reveal the presence of CNTs, bucky-onions and carbon nanopolyhedra, filled with α-Fe, Fe2O3 and Fe3O4. The carbon formed inside the pores of PVG was extracted from the glassy matrix yielding thin and short CNTs or structures resembling carbon foam. The preparative method opens up new avenues for iron oxide filled-CNT and bucky-onions synthesis.
Comparing photoinduced vibrational coherences in bacteriorhodopsin and in native and locked retinal protonated Schiff bases by Bixue Hou; Noga Friedman; Michael Ottolenghi; Mordechai Sheves; Sanford Ruhman (549-555).
Low frequency excited state vibrational coherences induced by impulsive photoexcitation in bacteriorhodopsin are detected via femtosecond pump–probe spectroscopy, and compared with similar data in retinal protonated Schiff bases of native and locked retinals. At delays above ∼100 fs a single vibration below 200 fs dominates the detected spectral modulations. Its frequency of ∼120 in retinal protonated Schiff base is virtually unchanged by locking the C13C14 bond in the trans or cis configurations, but is increased to 170 cm−1 within the protein environment. The implications of this result on the part played by the protein in directing the reactivity of the retinal within bacteriorhodopsin is discussed.
Quantum chaotic behavior in vibro-roto-torsional levels of methanol and its isotopomers by Domenico Marchesan; Giovanni Moruzzi; Naseem Rahman (556-564).
A statistical analysis of experimental vibro-roto-torsional energy levels of CH3OH, CD3OH, CH3OD, 13CH3OH and 13CD3OH molecules is performed, calculating the nearest neighbor spacing level distribution and the Dyson–Metha Δ3(L). The interactions among the molecular internal motions are clearly proved by the departure of the statistics from the regular spectral behavior, in particular for the CH3OD molecule, for both the NNLSD and the Δ3(L). Increasing the torsional number n, an increasing in the irregularity of the spectra is also observed, accounting for a stronger interaction among the internal and global rotation. Strong differences are seen in the statistics of the various isotopomers, claiming for a future more accurate and conclusive study of the isotopic dependence in the global molecular energy levels dynamics.
Calculations for the ground states of positronium halides by singly and doubly excited configuration interaction method by Shiro L Saito (565-571).
Singly and doubly excited configuration interaction calculations for the ground states of positronium halides, PsF, PsCl, PsBr, and PsI, are performed, and positron ionization energies, positronium binding energies, and two-photon annihilation rates are reported. It is shown that the correlation effects increase their values calculated by the Hartree–Fock method. In particular, the increases of the two-photon annihilation rates are very large.
Quantum-controlled color: chirp- and polarization-sensitive two-photon photochromism of spiropyrans in the solid phase by S.O. Konorov; D.A. Sidorov-Biryukov; I. Bugar; D. Chorvat; D. Chorvat; A.M. Zheltikov (572-578).
Phase and polarization control over photochromism in solid-state polymer materials doped with spiropyran compounds is demonstrated. Photochromism induced in spiropyrans by two-photon absorption of femtosecond pulses is shown to be sensitive to the initial chirp and polarization of these pulses. Enhancement of photochromism achieved by means of chirp and polarization control allows the yield of colored-form spiropyran to be increased by more than an order of magnitude.
Carbon-assisted synthesis of silicon nanowires by Gautam Gundiah; F.L. Deepak; A. Govindaraj; C.N.R. Rao (579-583).
Carbon-assisted synthesis of silicon nanowires has been accomplished with silicon powders as well as solid substrates. The method involves heating an intimate mixture of silicon powder and activated carbon or a carbon coated solid substrate in argon at 1200–1350 °C, and yields abundant quantities of crystalline nanowires. Besides being simple, the method eliminates the use of metal catalysts.
A DFT based ligand field model for magnetic exchange coupling in transition metal dimer complexes: by M Atanasov; C.A Daul (584-591).
The DFT based ligand field model for magnetic exchange coupling proposed recently, has been extended to systems containing more than one unpaired electron per site. The guidelines for this extension are described using a model example – the complex (NH3)3CrIII(OH)3CrIII (NH3)3 3+. The exchange Hamiltonian, H ex =−J12 S 1 S 2 has been simplified using symmetry principles, i.e. utilizing the D3h(C3v) CrIII – dimer(site) symmetry. Both antiferro- and ferromagnetic exchange coupling constants are found to yield important contributions to the value of the (negative, antiferromagnetic) exchange coupling constant in good agreement with experiment.
Structural model of the voltage-gated potassium channel Kv1.1 and molecular docking of Tc1 toxin from Tityus cambridgei to KcsA and Kv1.1 by Hsuan-Liang Liu; Jin-Chung Lin (592-597).
In this study, structural model of the pore loop region of the voltage-gated potassium channel Kv1.1 was constructed based on the crystallographic structure of KcsA. Subsequently, molecular docking experiments of Tc1 towards KcsA as well as Kv1.1 were performed. Tc1 forms the most stable complexes with these two channels when the side chain of K14 occupies the first K+ binding site. Tc1 binds preferentially towards Kv1.1 than KcsA due to the stronger electrostatic and hydrophobic interactions. Furthermore, surface complementarity of the outer vestibules of the channel to the Tc1 spatial conformations also plays an important role in stabilizing these Tc1/channel complexes.
Spectroscopic properties of Nd3+ ions in La2(WO4)3 crystal by Yujin Chen; Xiuqin Lin; Zundu Luo; Yidong Huang (598-604).
The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd3+ ions in anisotropic monoclinic crystal La2(WO4)3 were measured at room temperature. Taking the optical anisotropism into account, the spectroscopic parameters, such as intensity parameters Ωt (t=2,4,6), spontaneous emission probability, fluorescence branching ratio, radiative lifetime and fluorescence quantum efficiency were obtained by the Judd–Ofelt theory. The stimulated emission cross-section at 1058 nm wavelength was calculated to be 1.12 × 10−19 cm2. The good spectroscopic properties show that the Nd3+:La2(WO4)3 crystal is a good candidate of solid-state laser and self-stimulated Raman laser media.
Influences of hole blocking bathocuproine layer on emission of organic light emitting devices by Heqing Tang; Haixing Liao; Lihua Zhu (605-608).
Influences of an inserted hole-blocking bathocuproine (BC) layer were investigated on electroluminescence (EL) performances of organic light emitting devices with a configuration of ITO/BC/Alq3/Mg–Ag, where Alq3 is tris(8-quinolinolato)aluminum(III). Variations in the thickness of organic layers and bias voltages were found to alternate the emissive region from the BC layer to the Alq3 layer, resulting in shift of the emission wavelength in the EL spectra of the devices.
Photo-double ionization of HBr and DBr studied by threshold photoelectrons coincidence spectroscopy by Andrew J. Yencha; Antonio M. Juarez; Siu Pui Lee; George C. King (609-616).
Photo-double ionization of HBr and DBr has been investigated in the 32–37 eV energy range using synchrotron radiation and the threshold photoelectrons coincidence (TPEsCO) method. The TPEsCO spectra of HBr and DBr, encompassing the formation of the X 3Σ−, a 1Δ and b 1Σ+ states of HBr2+ and DBr2+, were recorded using a pair of penetrating-field electron spectrometers. All electronic band systems exhibited vibrational structure. In addition, the threshold photoelectron spectra of HBr and DBr for the formation of singly charged HBr and DBr were recorded simultaneously.
Photodissociation of bromobenzene at 267 and 234 nm: experimental and theoretical investigation of the photodissociation mechanism by Bifeng Tang; Rongshu Zhu; Ying Tang; Lei Ji; Bing Zhang (617-622).
The photodissociation of bromobenzene at 267 and 234 nm was investigated with time-of-flight (TOF) mass spectrometry. After the photodissociation, smaller branching ratios Br*(2P1/2)/Br (2P3/2) of bromobenzene, compared to that of 1-bromoheptane, were observed by subsequent (2 + 1) resonance-enhanced multiphoton ionization (REMPI) processes. The reduction of the branching ratio can be explained by a different photodissociation mechanism of aryl halides from that of alkyl halides. Also, the branching ratio of bromobenzene decreases with the reducing of the laser wavelength. Based on this finding and our ab initio calculations, a possible photodissociation mechanism of bromobenzene was proposed.
The HF2 −–CH3CH2OH complex: a theoretical study by I.P. Hamilton; G.P. Li (623-627).
Two minimum energy structures of the HF2 −–ethanol complex are examined. Both have a strong F⋯H–O and weak F⋯H–C hydrogen bond. For the lower energy structure the F⋯H–C bond involves an H atom of the CH3 group. The binding energy is 19.6 kcal/mol and the blue shift of the F–H–F asymmetric stretch is 746 cm−1. For the other structure, which is only 0.6 kcal/mol higher, the F⋯H–C bond involves an H atom of the CH2 group. This structure has an entropic advantage of +2.4 cal/mol/K and the Gibbs energies of the two structures are essentially identical at 298 K.
Direct synthesis of 2H–SiC nanowhiskers by Y. Yao; S.T. Lee; F.H. Li (628-633).
We report here the first synthesis of 2H-polytype silicon carbide (SiC) nanowhiskers by the reaction of silicon monoxide (SiO) with methane. The diameter of the 2H–SiC nanowhiskers was less than 200 nm and the length was over 2 μm. Energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), high resolution TEM (HRTEM) and Raman scattering spectroscopy were used to characterize the nanowhiskers. Electron diffraction and HRTEM confirmed that the nanowhiskers were composed of the rare-occurring 2H–SiC polytype with a 3C–SiC polytype tip. The growth direction of the nanowhiskers was along the hexagonal [0 0 0 1] orientation. The nanowhiskers had many stacking faults and micro-twins, which possibly caused the downshift of the Raman scattering peaks. The SiC nanowhiskers are believed to form via the oxide-assisted growth process.
High-resolution NMR spectroscopy in inhomogeneous B 0 and B 1 fields by two-dimensional correlation by Sasa Antonijevic; Stephen Wimperis (634-641).
Recently, there has been much interest in methods for obtaining high-resolution NMR spectra in inhomogeneous B 0 and B 1 fields and in their application to so-called ‘ex situ’ spectroscopy, where the sample and magnet/probe assembly are spatially separated. Here we discuss the implementation of the well-known two-dimensional nutation experiment as a method for correlating B 0 and B 1 inhomogeneities and, hence, achieving a high-resolution NMR spectrum. The advantages of this approach lie in its simplicity, its spatial (‘depth’) resolution, and in its not requiring a linear correlation of fields, i.e., B 1=αB 0+k, across the sample.
Coherent two dimensional spectroscopy with triply vibrationally enhanced infrared four-wave mixing by Kent A. Meyer; Daniel M. Besemann; John C. Wright (642-649).
A triply vibrationally enhanced four-wave mixing method measures the frequency domain coherent two dimensional vibrational spectrum of Ni(CO)2(PPh3)2 and Ni(CO)3PPh3 by triply vibrationally enhanced four-wave mixing using two excitation frequencies. This technique probes the coupling between vibrational modes. Two different phase-matching geometries were used. One geometry involves single vibrational quantum transitions while the second involves at least one multiquantum transition. Strong cross-peaks were observed for the phase-matching geometry requiring single quantum transitions but no measurable cross-peaks were observed for the multiquantum phase-matching geometry.
Cooperative effect in electron transfer between metal substrate and organized organic layers by Victor S. L’vov; Ron Naaman; Vasil Tiberkevich; Zeev Vager (650-653).
A model is given that shows that the electronic properties of close packed organized organic layers, adsorbed on conductive substrate, may be very different from the properties of the single adsorbed molecule. The difference arises from a cooperative effect that results in electron transfer between the substrate and the layer. It is induced when molecules having dipole moment and low polarizability are organized so that their dipole moment is perpendicular to the surface. The thermodynamics of the problem is described. The model provides a possible rationalization to recent observed new experimental properties of adsorbed organized organic layers.
Preferential sub-surface occupation of atomic hydrogen on Cu(1 1 1) by M.F. Luo; D.A. MacLaren; I.G. Shuttleworth; W. Allison (654-659).
We demonstrate sub-surface absorption of hydrogen on Cu(1 1 1) to be energetically favoured, even in the limit of zero coverage and without surface reconstruction. Helium atom scattering measurements indicate desorption of hydrogen from the surface at a lower temperature, than that required to remove all absorbed hydrogen. The stablest bonding site, which is invisible to the helium beam, is therefore not a surface site. Our experimental observations of the behaviour of Cu(1 1 1) differ from previous calculations and contrast with other systems, where population of subsurface sites generally occurs only after population of surface states, or after significant surface reconstruction.
DFT study of the reaction proceeding in the cytidine deaminase by Pawel Kedzierski; W.Andrzej Sokalski; Hansong Cheng; John Mitchell; Jerzy Leszczynski (660-665).
The deamination of cytidine performed by cytidine deaminase has been modeled using density functional theory yielding a reaction mechanism differing from that previously reported using semiempirical results. The main difference consists in the initial reaction step starting with Zn-bound water and N3-protonated cytidine. This study allows for the first time to close complete reaction cycle for the investigated process.
Excellent ambipolar photoconductivity of PVK film doped with fluoroperylene diimide by Min-Min Shi; Hong-Zheng Chen; Jing-Zhi Sun; Jian Ye; Mang Wang (666-671).
We report a novel bipolar charge transport material in a single-layer photoreceptor. Using the so-called photoinduced xerographic discharge technique, photoconductivity of the material was measured in positive charging and negative charging conditions, respectively. In both cases, it exhibited excellent photoconductivity. The material was obtained by doping poly(N-vinyl carbazole) (PVK) with a novel organic electron acceptor of N,N ′-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (DFPP). The combined efforts of UV–Vis absorption, DSC, XPS and cyclic voltammetry characterizations demonstrated that D–A complex was formed between DFPP (A) and PVK (D) due to their different electron affinities. The data also suggested that electron transport channels composed of DFPP molecules might exist in the film, providing the film not only high exciton dissociation efficiency but also good electron transport ability. The electronic and structural properties of the DFPP-doped PVK film are also reported.
Computing potential energy curve for hydrogen fluoride in Ornstein-Uhlenbeck diffusion quantum Monte Carlo method by Shih-I Lu (672-676).
The potential energy curve of hydrogen fluoride was calculated using the Ornstein-Uhlenbeck diffusion quantum Monte Carlo method. There are two choices in the determination of the trial wave function: a full optimization of all parameters of the trial wave functions and a partial optimization of the coefficients of different configuration wave functions. A full optimization gave an excellent result while comparing with results of other theoretical calculations as well as the experiment. A partial optimization described a wrong behavior in large separation but provided a good alternative in calculating the behavior near the equilibrium distance while considering the computational demandings.
Second-order nonlinearity in bulk azodye-doped hybrid inorganic–organic materials by nonresonant all-optical poling by Jiayu Guo; Jinhai Si; Guodong Qian; Jianrong Qiu; Minquan Wang; Kazuyuki Hirao (677-682).
Azodye-doped vinyl group substituted bulk silica materials were prepared by a sol–gel method. Photoinduced noncentrosymmetry in these initially centrosymmetric rigid matrixes was demonstrated first using nonresonant all-optical poling with a fundamental light at wavelength of 1500 nm and its second-harmonic light. The largest photoinduced second-order nonlinear optical coefficient d 33 was estimated to be 8×10−3 pm/V. The characteristic kinetics of decay of the induced second-order susceptibility was measured by second-harmonic generation. Although the signal decay was fast and the coefficient d 33 was low, we found that increasing the power of the seeding beams could improve the second-harmonic signal decay process.
Electronic properties of giant fullerenes and complex graphitic nanostructures with novel morphologies by Florentino López-Urı́as; Mauricio Terrones; Humberto Terrones (683-690).
Using a Hückel approach we study the electronic properties of large graphitic nanostructures: giant quasi-spherical fullerenes, chiral and non-chiral icosahedral giant fullerenes, holey balls, finite and toroidal carbon nanotubes. We found this model describes accurately the electronic characteristics of novel sp2 carbon systems, requiring less computational effort when compared to multi-band tight-binding methods. We calculate the density of states (DOS) and the electronic charge distribution of these structures. Our calculations could lead to the development of novel electronic and field emission devices using complex sp2-like carbon architectures.
A flexible top-emitting organic light-emitting diode on steel foil by Zhiyuan Xie; Liang-Sun Hung; Furong Zhu (691-696).
An efficient flexible top-emitting organic light-emitting diode (FTOLED) was developed on a thin steel foil. The FTOLED was constructed on the spin-on-glass (SOG)-coated steel substrate with an organic stack of NPB/Alq3 sandwiched by a highly reflective Ag anode and a semitransparent Sm cathode. An ultrathin plasma-polymerized hydrocarbon film (CFX) was interposed between the Ag anode and the NPB layer to enhance hole-injection, and an additional Alq3 layer was overlaid on the Sm cathode to increase light output. The FTOLED showed a peak efficiency of 4.4 cd/A higher than 3.7 cd/A of a convention NPB/Alq3-based bottom-emitting OLED.
Dynamics of solvent relaxation in room temperature ionic liquids by Debdeep Chakrabarty; Partha Hazra; Anjan Chakraborty; Debabrata Seth; Nilmoni Sarkar (697-704).
In this Letter, the steady state and time resolved emission behaviour of two solvatochromic Coumarin dyes (Coumarin 153 and Coumarin 152) in two room temperature ionic liquids ([bmim][PF6] and [hmim][PF6]) are reported. The solvent relaxation in these ionic liquids is biphasic and retards drastically compared to conventional solvents of similar polarity. The motion of the ions is responsible for solvation in these ionic liquids. The rotational relaxation of both the dyes is also retarded in these ionic liquids in comparison to that of conventional solvents. The high viscosity of these ionic liquids is possibly responsible for the slow rotational relaxation.
Second-harmonic generation as a probe of conformational change in molecules by J.S Salafsky (705-709).
Optical second-harmonic generation has been used to detect a ligand-induced conformational change in a protein. The protein was made second-harmonic active by labeling it with a second-harmonic active dye. The conformational change was detected in a monolayer of the protein at the air–water interface.
Surfactant-assisted nanoparticle assembly of mesoporous β-FeOOH (akaganeite) by Zhong-Yong Yuan; Bao-Lian Su (710-714).
A new mesoporous form of crystalline β-FeOOH (akaganeite) was successfully prepared by a technology of surfactant-assisted nanoparticle assembly in the presence of a nonionic PEO-surfactant. The synthesized mesoporous β-FeOOH has a high surface area of 228 m2/g and a pore size of 4.3 nm with a hierarchical scaffold-like structure formed through the aggregation and intergrowth of akaganeite nano-rods. To our knowledge, this is first known report of mesostructured crystalline akaganeite material. Thermal treatment at 200 °C afforded the retention of the akaganeite structure. A complete transformation to hematite occurred after calcination at 300 °C with structural collapse.
GaN-filled carbon nanotubes: synthesis and photoluminescence by C.Y. Zhi; D.Y. Zhong; E.G. Wang (715-719).
Employing a GaAs substrate, GaN nanowires encapsulated in carbon nanotubes are synthesized by microwave-plasma-enhanced chemical vapor deposition. Almost 100% of the carbon nanotubes are filled with GaN. Both high-resolution transmission electron microscopy and selected area electron diffraction pattern reveal high crystallization in the GaN nanowires. The formation mechanism of the GaN-core/C-shell structure is discussed, emphasizing chemistry’s influence on the structure produced, particularly the role of Ga from the substrate. Photoluminescence measurements reveal an ultraviolet band located at 3.35 eV and a yellow band located at 2.20 eV. The redshift of the ultraviolet band is attributed to N vacancies that result from the Ga-rich conditions of growth.
Theoretical study of low-lying electronic states of BP molecule by Beatriz Miguel; Salama Omar; Paula Mori-Sánchez; José M. Garcı́a de la Vega (720-724).
BP is a molecule that, to date, has not been experimentally characterized. However, theoretical calculations yield a stable molecule, although its ground state is not unequivocally determinated. In this work, potential energy curves for the ground state and the lower excited states of BP molecule have been calculated. They are derived using the MRDCI procedure and employing 6-311+G(2df) basis sets. The spectroscopic constants and excitation energies for the bound states of BP are compared with previous theoretical results. The MRDCI calculations give the 3 Π state as the ground state, with R e=1.747 Å, D e=3.15 eV and ω e=954 cm−1.
Spectroscopic characterization of the F1Π1 ‘Rydberg’ state of the MgO molecule by D Bellert; Katherine L Burns; Nguyen-Thi Van-Oanh; Jinjin Wang; W.H Breckenridge (725-728).
The F1Π1 ‘Rydberg’ state of 24Mg16O has been characterized by two-color Resonance-Enhanced Two-Photon Ionization (R2PI) spectroscopy in the 37 000–39 000 cm−1 region. Several rotationally resolved bands, assigned to 24Mg16O(F1Π1 ← X1Σ+) vibronic transitions, have been analyzed to yield spectroscopic constants for the F1Π1 state. Consistent with the ab initio calculations of Peyerimhoff and co-workers, the F1Π1 state appears to have mixed Rydberg–valence character.
Interaction energies in stacked DNA bases? How important are electrostatics? by Glake Hill; Gareth Forde; Nicholas Hill; William A. Lester; W. Andrzej Sokalski; Jerzy Leszczynski (729-732).
For the first time, the physical nature of intermolecular interactions between 10 DNA stacked bases has been examined by an interaction energy decomposition method based on the variation–perturbation theory. The dominant correlation term including dispersion interactions is found to be cancelled to a considerable extent by exchange and delocalization contributions leaving the relatively smaller long range electrostatic contribution as the most important factor determining relative stacking interaction energies. The electrostatic multipole component closely mimics the trend of total interaction energy in all considered systems.
Excited state dynamics of β-carotene explored with dispersed multi-pulse transient absorption by Delmar S. Larsen; Emmanouil Papagiannakis; Ivo H.M. van Stokkum; Mikas Vengris; John T.M. Kennis; Rienk van Grondelle (733-742).
The excited-state dynamics of β-carotene in hexane was studied with dispersed ultrafast transient absorption techniques. A new excited state is produced after blue-edge excitation. Pump–repump–probe and pump–dump–probe measurements identified and characterized this state, termed S ‡ , which exhibits a blue-shifted spectrum with a longer lifetime than S1. We establish the independent co-existence of the S ‡ and S1 states following the relaxation of S2 and demonstrate that S ‡ is an electronically excited state and not a vibrationally excited ground-state species. Our data support the premise that S ‡ is formed directly from S2 and not via preferential excitation of ground-state sub-populations.
On the role of the conical intersection in H + H2 reactive scattering by Juan Carlos Juanes-Marcos; Stuart C. Althorpe (743-750).
The hydrogen exchange reaction has a conical intersection and is therefore a prototype for studying geometric phase effects in reaction dynamics. We compute wave packets in hyperspherical coordinates for the reaction H + H2 (v 0=0,j 0=0) → H2 + H, over the collision energy range E coll=0.75−2.02 eV, using the plane wave packet method. Geometric phase effects are not included. The wave packets visualise the quantum dynamics around the conical intersection and relate it to the centre-of-mass scattering angle. The wave packet fails to encircle the conical intersection, making slightly less than half a revolution. This provides a physical picture for why geometric phase effects in this reaction are expected to be reduced.
Probing of bound electron–hole-pairs by optical re-excitation in a short-chain oligomer by L. Lüer; G. Cerullo; M. Zavelani-Rossi; G. Lanzani (751-758).
We probe the photoconductive response to optical re-excitation of photoexcitations in a four-member oligophenylenevinylene in a sandwich LED configuration. Re-excitation of the singlet exciton leads to an enhancement of photocurrent (PC). Only excitons in the vicinity of the aluminum electrode give rise to PCs. Also charged photoexcitations can be re-excited to form mobile charge carriers. We show that an increase of PC is only observed during the ultrashort period of geminate recombination, due to optically induced enhancement of the escape probability of the charged pairs.
Temperature and solvent effects on the photodynamics of 1′-hydroxy-2′-acetonaphthone by J.A. Organero; A. Douhal (759-765).
We present studies of temperature viscosity and polarity effects on the photodynamics of 1′-hydroxy-2′-acetonaphthone. We observed a striking temperature effect on the non-radiative decays and which explains the low emission quantum yield of the formed keto-type phototautomers. The thermal activation energy is lower for the keto structure (0.96 kcal/mol) than for the keto rotamer one (3.4 kcal/mol). For the alcohols family of solvents, the keto-type tautomer is more sensitive to solvent response than the keto rotamer. However for non-hydroxylic media the low influence of solvent polarity is similar for both keto type structures.
Kinetics of the reaction of the CCl2 biradical with NO by Alexander A. Shestov; Sofya A. Kostina; Eugene V. Shafir; Irene R. Slagle; Vadim D. Knyazev (766-770).
The kinetics of the of CCl2 with nitric oxide has been studied using the laser photolysis/photoionization mass spectrometry technique. Dichloromethylene biradicals were produced by the pulsed laser photolysis of carbon tetrachloride and the kinetics of their decay due to reaction with NO were monitored in direct time-resolved experiments. The temperature dependence of the rate constant (300–750 K) can be described by the Arrhenius expression k1=(1.12±0.18)×10−12 exp(−(312±74) K/T) cm3 molecule−1 s−1. Rate constants are independent of the bath gas density within the experimental range, [He] = (3–12) × 1016 atom cm−3. ClCNO was observed as a product of the reaction.
Standard thermodynamic properties of solutes in supercritical solvents: simulation and theory by J.L Alvarez; R Fernández-Prini; E Marceca (771-776).
We report a modified simulation procedure to calculate partial molar quantities of dilute solutions in supercritical fluids through the Krichevskii function. This procedure circumvents the difficulties posed by the very large solvent compressibility and expansivity in the near-critical region of the solutions where other simulation procedures cannot be used.
Extensive, high-resolution measurement of hyperfine interactions: precise investigations of molecular potentials and wave functions by Lisheng Chen; Jun Ye (777-783).
We report high-resolution and high-precision measurement of hyperfine interactions of the first excited electronic state (B) of I2 over an extensive range of vibrational and rotational quantum numbers. Systematic variations in the hyperfine parameters, including both rovibrational level dependence and internuclear separation dependence, are confirmed by calculations based on ab initio molecular potential energy curves and electronic wave functions derived from a separated-atom basis set. We have accurately determined the state-dependent quantitative changes of hyperfine interactions caused by perturbations from other electronic states and identified the respective perturbing states.
Author Index (784-797).