bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and probing of alignment in molecular ensembles by saturated coherent pulsed laser excitation
Authors: Meyer Henning , Leone Stephen R.
Published: July 2002

An analytical solution of the optical Bloch equations for a degenerate two-level system is presented for coherent excitation with a monochromatic light pulse of rectangular time profile and linear polarization including off-resonance interaction. The generalization to an arbitrary excitation and detection geometry is achieved by incorporation of the appropriate coordinate frame rotations. In this way the formalism can be applied to the determination of alignment parameters in molecular ensembles even under partially saturated conditions. In the limit of linear absorption the results reduce to those obtained by Greene and Zare [J. Chem. Phys. 78, 6741 (1983)]. For complete saturation on lines of a Q or R branch, polarized fluorescence detection is sensitive only to the quadrupole alignment moment. The formalism also allows investigation of the production of aligned ensembles via coherent optical pumping with a single pulse. Depending on the degree of saturation as well as the detuning from resonance, strong alignment can be created.
Molecular dynamics simulations of sliding friction of Langmuir–Blodgett monolayers
Authors: Koike A. , Yoneya M.
Published: July 2002

Molecular dynamics simulations have been used to study friction in Langmuir–Blodgett monolayers of perfluorocarboxylic acid and hydrocarboxylic acid on SiO2. The frictional force of perfluorocarboxylic acid is found to be about three times as large as that of hydrocarboxylic acid. The qualitative aspects of this simulation results are consistent with known experimental results. In order to interpret the difference in the frictional force, a series of simulations have been carried out by changing molecular potential parameters. The simulation results suggest that the 1–4 van der Waals interaction is the main cause of the larger frictional force for perfluorocarboxylic acid than that for hydrocarboxylic acid. The results also show that frictional force is roughly proportional to the excess root mean square fluctuation of the potential energy under shear from the equilibrium. The relation between the frictional force and the energy needed for molecular deformation under shear condition is also discussed.
Quasiclassical trajectory study of the H+D2→HD+D reaction at a collision energy of 2.2 eV: A comparison with experimental results
Authors: Aoiz F. J. , Bañares L. , Herrero V. J.
Published: July 2002

Simulations of the available experimental results for the H+D2→HD+D reaction at 2.2 eV collision energy, have been carried out using quasiclassical trajectory (QCT) calculations on ab initio potential energy surfaces. Although there are some differences between experiment and theory, the global description of the measurements provided by the QCT approach is reasonably good considering the uncertainty of the data. Higher resolution studies would be desirable in order to clarify the apparent discrepancies.
Ultraviolet photodissociation of the HCCO radical studied by fast radical beam photofragment translational spectroscopy
Authors: Mordaunt David H. , Osborn David L. , Choi Hyeon , Bise Ryan T. , Neumark Daniel M.
Published: July 2002

The ultraviolet photolysis of jet-cooled mass-selected ketenyl radicals has been investigated using the technique of fast radical beam photofragment translational spectroscopy. The C̃2Π(2A″)–X̃2A″ photofragment yield cross section spans 33 400–48 000 cm−1 and exhibits resolved resonances and broad continua. Dissociation produces both ground and excited state CH radicals in association with ground state CO fragments; there is no evidence for H atom elimination. Analysis of the photofragment kinetic energy release spectra yield a value for the C–C bond dissociation energy and heat of formation of HCCO: D0(HC–CO)=3.14±0.03 eV (72.4±0.7 kcal/mol) and ΔHf,00(HCCO)=1.82±0.03 eV (42.0±0.7 kcal/mol).
Scaling behavior of diffusion limited annihilation reactions on random media
Authors: de Albuquerque Édler L. , Lyra Marcelo L.
Published: July 2002

We investigate numerically the kinetics of diffusion limited annihilation reactions in disordered binary square lattices where the reacting particles are constrained to diffuse on a concentration p of the lattice sites. We find that the asymptotic decay of the particle concentration in the percolative regime is of the form c(t,p)−cr(p)∝t−ds/2, where cr(p) is the concentration of residual particles. We recover well known results such as ds(p≳pc)=d=2 with logarithmic corrections, and ds(pc)=1.34±0.02. For p<pc we employ a scaling theory and collapse the data onto a universal form dc/dt=τ−(ds(pc)/2+1)f(t/τ), with τ being a characteristic diffusion time and f(t/τ) representing the crossover from a power law decay to a stretched exponential one. We relate the present results with the kinetics of the excitation reaction (triplet + triplet → singlet) on isotopic mixed crystals of naphthalene.
Recursive density-matrix-spectral-moment algorithm for molecular nonlinear polarizabilities
Authors: Tretiak Sergei , Chernyak Vladimir , Mukamel Shaul
Published: July 2002

An iterative algorithm is developed for calculating nonlinear optical polarizabilities using a series of generalized sum rules that resemble the Lanczos algorithm and connect spectral moments of the driven single-electron density matrix to ground state charge distributions and bonding network. The size scaling and saturation of off-resonant polarizabilities (up to seventh order) of polyacetylene oligomers with up to 300 carbon atoms is analyzed in terms of collective electronic oscillators. Simple analytical expressions for size and bond-length alternation dependence of off-resonant polarizabilities are derived using a single-oscillator approximation.
Theory of continuum mediated two-photon ionization, with applications to CH3I
Authors: Abrashkevich D. G. , Shapiro M.
Published: July 2002

Theory of two-photon ionization via intermediate dissociative states is developed. The theory is applied to the one-color two-photon ionization of CH3I for which the 3Q0 and 1Q1 dissociative states serve as intermediate resonances. Both CW and transient ionization spectra are calculated. The computed methyl iodide CW ionization line intensities are in profound disagreement with line intensities derived from two-photon zero kinetic energy electrons (ZEKE) experiments. The discrepancy may be viewed as evidence that ZEKE line-intensities are not simply proportional to the population of the ionic-core states. This extra dependence on the ionic-core states, most likely due to the existence of external ions, can be accounted for by comparing our calculations to the observed ZEKE line intensities. The dynamics revealed by ultrashort pulsed two-photon ionization is also studied. In methyl iodide, we find that pulses capable of revealing ‘‘real-time’’ dissociative dynamics must be considerably shorter than 50 fs.
Counting linear polyenes by excluding structures with steric strain
Authors: Yeh Chin-yah
Published: July 2002

Isomers of linear polyenes are counted by excluding structures of immediate steric strain, namely, those with any occurrence of three or four consecutive cis configurations.
Comment on ‘‘Comparison of positive flux operators for transition state theory using a solvable model’’ [J. Chem. Phys. 104, 7015 (1996)]
Authors: Miller William H.
Published: July 2002

The Weyl definition of the positive component of the flux operator is discussed. Specifically, it is noted that the imaginary part of the operator makes no contribution to the quantum mechanical transition state theory rate constant, and this is why it was omitted in previous work on the topic.
A quantum model for water: Equilibrium and dynamical properties
Authors: Lobaugh J. , Voth Gregory A.
Published: July 2002

Path integral molecular dynamics and centroid molecular dynamics have been applied to study and modify an empirical flexible model for water, the simple point charge/flexible (SPC/F) model. The quantum structural, thermodynamic and dynamical properties have been calculated and compared to their classical counterparts, as well as to experiment. The path integral molecular dynamics simulations demonstrate that the quantum liquid is less structured and exhibits less hydrogen bonding than its classical analog. Quantization also leads to a lower dielectric constant, relative to the corresponding classical value. Centroid molecular dynamics has been used to calculate single molecule time correlation functions, the Debye dielectric relaxation correlation function, and the power spectrum for the quantum model. These time correlation functions decay more rapidly than the classical ones, indicating that nuclear rotational tunneling occurs in the liquid. The power spectrum of the quantized liquid also exhibits red shifted bend and stretch frequencies relative to the classical model. A modification of the parametrization of the harmonic intramolecular potential for the simple point charge/flexible (SPC/F) model is suggested and tested in order to improve the dielectric properties as well as the values of the vibrational frequencies. The quantum simulation of the modified water model, called SPC/F2, gives better agreement with the experimental IR spectrum of water and the measured value of the dielectric constant. However, the self-diffusion constant for the modified SPC/F model is still somewhat too large relative to experiment. In addition, the NMR rotational time constant is too small compared to experiment. While these discrepancies leave room for future modifications (e.g., including electronic polarizability), the model represents the first parametrization of an empirical flexible water potential explicitly developed for quantum path integral simulations.
Dynamics of the deactivation and desorption of Ba atoms from Ar clusters
Authors: Osborne M. A. , Gaveau M. A. , Gee C. , Sublemontier O. , Mestdagh J. M. , Visticot J.-P.
Published: July 2002

The Doppler profiles of Ba(3P2) atoms desorbed from the surface of argon clusters following the deactivation of Ba(1P1) have been measured. These measurements have been performed for desorption from pure ArN clusters and as a function of a known average number of CH4 molecules deposited on the cluster. Analysis of the profile widths with respect to the kinetic energy release from deactivation indicates that desorption occurs along a single Ba–Ar and Ba–CH4 coordinate in the former and latter cases, respectively. By comparing the kinetic energy distributions in the desorbed barium with the relative kinetic energy available at the temperature of the cluster it is found that the collisions leading to deactivation in both cases are gas kinetic at the temperature of the cluster (35 K). The residual anisotropies in the Doppler profiles reveal the Ba–Ar deactivation to be a relatively inefficient process allowing the barium to undertake a full migration on the cluster surface before desorbing. This results in an essentially isotropic distribution of recoil velocities. In contrast Ba–CH4 deactivation is sufficiently fast to preserve some degree of anisotropy in the desorbed barium velocity distribution. The anisotropy results from the depolarization of the barium orbital due to both the migration of the barium on the cluster surface and axial relaxation of the orbital by collisions with neighboring argon atoms. Calculations of the anisotropies resulting from both reorientating mechanisms show a significant degree of relaxation and migration to occur before the barium is desorbed.
Relaxation dynamics of multilevel tunneling systems
Authors: Neu Peter , Heuer Andreas
Published: July 2002

A quantum mechanical treatment of an asymmetric double-well potential (DWP) interacting with a heat bath is presented for circumstances where the contribution of higher vibrational levels to the relaxation dynamics cannot be excluded from consideration. The deep quantum limit characterized by a discrete energy spectrum near the barrier top is considered. The investigation is motivated by simulations on a computer glass which show that the considered parameter regime is “typical” for DWPs responsible for the relaxation peak of sound absorption in glasses. Relaxation dynamics resembling the spatial- and energy-diffusion-controlled limit of the classical Kramers’ problem, and Arrhenius-type behavior is found under specific conditions.
He scattering from random adsorbates, disordered compact islands, and fractal submonolayers: Intensity manifestations of surface disorder
Authors: Yinnon A. T. , Lidar (Hamburger) D. A. , Farbman I. , Gerber R. B. , Zeppenfeld P. , Krzyzowski M. A. , Comsa G.
Published: July 2002

A theoretical study is made on He scattering from three basic classes of disordered adlayers: (a) translationally random adsorbates, (b) disordered compact islands, and (c) fractal submonolayers. The implications of the results to experimental studies of He scattering from disordered surfaces are discussed, and a combined experimental-theoretical study is made for Ag submonolayers on Pt(111). Some of the main theoretical findings are: (1) The scattering intensities from the three disorder classes differ significantly, and can be used to distinguish between them. (2) Structural aspects of the calculated intensities from translationally random clusters were found to be strongly correlated with those of individual clusters. (3) For fractal islands, just as for all surfaces considered here, the off-specular intensity depends on the parameters of the He/Ag interaction, and does not follow a universal power law as previously proposed in the literature. In the experimental-theoretical study of Ag on Pt(111), we use experimental He scattering data from low-coverage (single adsorbate) systems to determine an empirical He/Ag–Pt potential of good quality. Then, we carry out He scattering calculations for high coverage and compare with experiments for these systems. The conclusion is that the actual experimental phase corresponds to small compact Ag clusters of narrow size distribution, with partial translational disorder.
Correlation formula for the couplings at crossings between ionic and covalent molecular states
Authors: Aquilanti Vincenzo , Cappelletti David , Pirani Fernando
Published: July 2002

From an analysis of empirical and theoretical information on ionic and covalent interactions, a relationship is established between the coupling matrix elements (which measure the nonadia-batic splitting at avoided crossings and strongly influence transition probabilities) and basic quantities of separated partners (ionization potentials, electron affinities, polarizabilities). Although the systems considered here are limited to alkali atoms interacting with simple atoms and mole-cules, the proposed correlation rule paves the way for extensions to deal with electron transfer reaction dynamics for more general donor-acceptor couples.
Experimental observations of high-energy electron degradation in argon
Authors: Burgers Manuela M. , Cooper Ronald
Published: July 2002

Pulse radiolysis and emission spectroscopy techniques have been used to examine the production of the 2p1 state of Ar and the 4p 2P1/2 and 4p 2D5/2 states of Ar+ at gas pressures below 1 Torr. The rate of formation of these states has been compared with the results from calculations using the time-dependent Spencer–Fano theory of high-energy electron degradation. It is found that the theory successfully predicts the time scale of events in pulse-irradiated argon gas.
Two phases of acetylene adsorbed on NaCl(001) studied by high-resolution helium atom scattering
Authors: Glebov Alexei , Miller Roger E. , Toennies J. Peter
Published: July 2002

High-resolution helium atom scattering (HAS) has been used to identify two stable phases of acetylene physisorbed on NaCl(001). Deposition at a surface temperature Ts=90 K gives rise to a single stable low density phase (phase I). At Ts=80 K phase I formed first, but growth continues to form a second, higher density phase. At Ts≈50 K we observe layer by layer growth up to at least five layers of acetylene. The symmetries of the high and low temperature phases have been determined from HAS diffraction patterns. Structural models for both phases are proposed based upon the results of the HAS and previous IR studies. Adsorption of C2D2 on NaCl(001) has also been investigated. No differences in the structures of C2D2 and C2H2 monolayers were observed.
Photodissociation dynamics of HCl in solid Ar: Cage exit, nonadiabatic transitions, and recombination
Authors: Krylov Anna I. , Gerber R. Benny
Published: July 2002

The photodissociation of HCl in solid Ar is studied by non-adiabatic Molecular Dynamics simulations, based on a surface-hopping treatment of transitions between different electronic states. The relevant 12 potential energy surfaces and the non-adiabatic interactions between them were generated by a Diatomics-in-Molecules (DIM) approach, which incorporated also spin-orbit coupling. The focus of the study is on the non-adiabatic transitions, and on their role both in the cage-exit of the H atom, and in the recombination process. It is found that non-adiabatic transitions occur very frequently. In some of the trajectories, all the 12 electronic states are visited during the timescale studied. At least one non-adiabatic transition was found to occur even in the fastest cage-exit events. The other main results are: (1) The total yields for photofragment separation (by cage exit of the H atom) and for H+Cl recombination onto the ground state are roughly equal in the conditions used. (2) The cage exit events take place in the time-window between ∼70 fs and ∼550 fs after the excitation pulse, and are thus all at least somewhat delayed. The recombination events span a much broader time-window, from almost immediately after excitation, and up to ∼1100 fs and beyond. (3) The electronic energy relaxation events during the process depend significantly on symmetry and interactions of the states involved, and not only on the energy gaps between them. (4) Different electronic states reached in the course of the process exhibit different propensities with regard to the recombination versus cage exit outcome. (5) Spin-orbit interactions, and spin-forbidden transitions play an important role in the process, especially for recombination events.
Comment on: “Ab initio investigation of internal rotation in the ethylene-sulfur dioxide dimer” [J. Chem. Phys. 102, 4184 (1995)]
Authors: Sordo J. A.
Published: July 2002

It is shown that the basis set superposition error does not affect calculations on barriers to internal rotation. Such barriers must be computed directly as the energy difference between the transition state structure and the corresponding minimum.
Theoretical investigation of the potential energy surface for the NH2+NO reaction via density functional theory and ab initio molecular electronic structure theory
Authors: Diau Eric W.-G. , Smith Sean C.
Published: July 2002

The potential energy surface of the NH2+NO reaction, which involves nine intermediates (1–9) as well as twenty-three possible transition states (a–w), has been fully characterized at the B3LYP/cc-pVQZ//B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p)] and modified Gaussian-2 (G2M) levels of theory. The reaction is shown to have three different groups of products (HN2+OH, N2O+H2, and N2+H2O denoted as A, B, and C, respectively) and a very complicated reaction mechanism. The first reaction path is initiated by the N–N bond association of the reactants to form an intermediate H2NNO, 1, which then undergoes a 1,3-H migration to yield an isomer pair HNNOH (2,3) (separated by a low energy torsional barrier) which can then proceed along three different paths. Because of the essential role it would play kinetically, the enthalpy of the NH2+NO→HN2+OH reaction has been further investigated using various levels of theory. The best theoretical results of this study predicted it to be 0.9 and 2.4 kcal mol−1 at the B3LYP and CCSD(T) levels, respectively, using a relatively large basis set (AUG-cc-pVQZ) based on the geometry optimized at the B3LYP/6-311G(d,p) level of theory. It has been found that TS g(4→B) is expected to be the rate-determining transition state responsible for the NH2+NO→N2O+H2 reaction. TS g lies above the reactants by only 2.6 kcal mol−1 according to the G2M prediction. On the other hand, TS h(3→7) is a new transition state discovered in this work which may allow some kinetic contribution from the NH2+NO→N2+H2O reaction under high temperature conditions due to its relatively low energy as well as its loose transition state property. A modified G2 additivity scheme based on the G2(DD) approach has been shown to be necessary for better predicting the energetics for TS h, which gives a value of 2.3 kcal mol−1 in energy with respect to the reactants. Generally, the cost-effective B3LYP method is found to give very good predictions for the optimized geometries and vibrational frequencies of various species in the system if compare them with those optimized at the QCISD/6-311G(d,p) and 12-in-11 CASSCF/cc-pVDZ levels of theory. Furthermore, it is noticeable in this study that most of the relative energies calculated via the B3LYP method are more close to the G2M results than those predicted at the PMP4 and CCSD(T) levels using the same 6-311G(d,p) basis set.
Photoabsorption probability for a system governed by a time-dependent Hamiltonian through the (t,t′) formalism
Authors: Pang John W. , Neuhauser Daniel , Moiseyev Nimrod
Published: July 2002

Heller’s expression for the absorption cross-section in the weak field limit is extended to cases where the total Hamiltonian contains a strong time-dependent component, supplemented by a weak field. A very similar expression to the original case then results when the (t,t) formalism is used; one only needs to construct a correlation function for the system without the weak field, and use it to extract the absorption probability for any value of the weak-field frequency (or pulse shape). In addition, a numerical approach for extracting Floquet states without full-matrix diagonalization is demonstrated, by filtering (or filter-diagonalization) a single wave function (or the correlation function) propagated under the (t,t) Hamiltonian.
Extensive relativistic calculations on the palladium hydride molecule
Authors: Sjo/voll Merethe , Fagerli Hilde , Gropen Odd , Almlöf Jan , Saue Trond , Olsen Jeppe , Helgaker Trygve
Published: July 2002

The lower states of the PdH molecule have been studied with different relativistic methods. At the spin-free level, relativistic effects are shown to be crucial for a proper description of the molecule. PdH is shown to be a single-configuration molecule, but the configuration interaction (CI) results are highly sensitive to the choice of orbital basis. Spin–orbit interaction has been included through spin–orbit CI theory based on the second order Douglas–Kroll operator and through fully relativistic CI calculations based on the Dirac–Coulomb Hamiltonian. The results are in good agreement, but requires a proper choice of orbital basis in the spin–orbit CI calculation to ensure a balanced description of all ΛΣ states coupled by spin–orbit interaction.
Explicit expressions for triatomic Eckart frames in Jacobi, Radau, and bond coordinates
Authors: Wei Hua , Carrington Tucker
Published: July 2002

For triatomic molecules we derive expressions to relate any Eckart axis system with two axes in the molecular plane to simple molecule-fixed axis systems commonly used to derive kinetic energy operators. We express the orientation of an Eckart axis system in terms of Jacobi, Radau or bond coordinates.
Combined ab initio and density functional study on polaron to bipolaron transitions in oligophenyls and oligothiophenes
Authors: Irle Stephan , Lischka Hans
Published: July 2002

Ab initio self-consistent-field (SCF), two-configuration SCF (TCSCF), and density functional theory (DFT) calculations on the charge–transfer complexes of doubly Li/Cl-doped oligothiophenes and oligo(p-phenyls) and on respective charged systems without counterions have been carried out in order to study polaron to bipolaron transitions. Oligomer chains up to octamers and the ring structures cyclo-dodecathiophene and cyclo-dodeca(p-phenyl) have been investigated. Special attention is paid to the open-shell biradical character of two isolated polaronic defects. It is found that the TCSCF and the spin-unrestricted DFT methods can be successfully applied. A bipolaron structure is obtained when the doping atoms are located on neighboring rings and when there is one undoped ring separating the two doped ones. If there are two or more undoped rings in between a two-polaron configuration (biradical) is found. The bipolaron system is calculated to be more stable than the two-polaron case when counterions are taken into account. The stabilities are reversed if the bare, doubly-charged systems are considered. A theoretical estimate for the barrier height of the polaron to bipolaron transition is given using model reaction coordinates.
Solvation of the methoxy radical in small clusters
Authors: Fernandez J. A. , Yao J. , Bernstein E. R.
Published: July 2002

In this work we analyze clusters between the methoxy radical (CH3O, an open-shell molecule) and the nonpolar solvents Ar, N2, CH4, and CF4. CH3O is formed through the photolysis of CH3OH vapor in a supersonic expansion of CH3OH and a solvent gas (Ar, N2, CH4, CF4) seeded in a carrier gas of He. The radical and solvent molecules are cooled to ∼15–20 K and form clusters. These clusters are probed using laser induced fluorescence (LIF) of the CH3O radical. An extensive set of calculations, including ab initio and atom–atom potential calculations and rotational contour simulations are performed for each cluster in order to elucidate the cluster structure and the nature and relative importance of the limiting types of interactions that are responsible for cluster binding. A final minimum energy structure is presented for each cluster, together with the analysis of the limiting type of interactions that generate the van der Waals binding of the cluster.
Electronic spectroscopy of the R⋅SH (R=Ne, Ar, Kr) complexes
Authors: Yang Min-Chieh , Carter Christopher C. , Miller Terry A.
Published: July 2002

The laser induced fluorescence spectra of the thiohydroxyl radical inert gas complexes, R⋅SH (R=Ne, Ar, and Kr) are reported. The spectra of numerous isotopomers involving S32, S34, Kr84, Kr86, H1, and H2 have been observed. By using isotopic shifts of the heavy atoms, and other observations, the overwhelming majority of the 60 observed vibronic transitions have been assigned as originating from the vibrationless level of the X̃ Π2 state and terminating on specific vibrational levels (vSH, vbk, vs) of the Ã Σ+2 state, where nominally vs is the R-SH stretch, vSH is the SH monomer stretch, and vbk is the bending vibration. Vibrational frequencies, ωe, and anharmonicities, ωexe, for many of the modes are obtained, as well as dissociation energies (assuming a simple model) for both the Ã and X̃ states of the R⋅SH complexes.
Surface tension and phase coexistence properties of the lattice fluid from a virtual site removal Monte Carlo strategy
Authors: Provata Astero , Prassas Vassilis D. , Theodorou Doros N.
Published: July 2002

A thin liquid film of lattice fluid in equilibrium with its vapor is studied in 2 and 3 dimensions with canonical Monte Carlo simulation (MC) and Self-Consistent Field Theory (SCF) in the temperature range 0.45Tc to Tc, where Tc the liquid-gas critical temperature. Extending the approach of Oates et al. [Philos. Mag. B 61, 337 (1990)] to anisotropic systems, we develop a method for the MC computation of the transverse and normal pressure profiles, hence of the surface tension, based on virtual removals of individual sites or blocks of sites from the system. Results from implementation of this new method, obtained at very modest computational cost, are in reasonable agreement with exact values and other MC estimates of the surface tension of the 2-d and 3-d model systems, respectively. SCF estimates of the interfacial density profiles, the surface tension, the vapor pressure curve and the binodal curve compare well with MC results away from Tc, but show the expected deviations at high temperatures.
Total and direct correlations in the liquid–vapor interface and the capillary-wave theory
Authors: Stecki J.
Published: July 2002

The two-point total correlation function H̃(1,2)=〈δρ−kδρk〉=H(z1,z2,k) in the interfacial zone between a Lennard-Jones liquid and its coexisting vapor is determined in a molecular dynamics simulation at a low temperature T=0.75. New terms absent in the standard capillary wave theory are discovered. Eigenvector analysis and matrix partitioning of H and of the direct correlation function C revealed a strong k2 dependence at k→0 in a set of terms proportional to ρ′ρ′, ρ′′ρ′′, ρ′′′ρ′′′,… . The bending coefficient is found nonexistent. Projections of H, C, and susceptibilities are discussed in the context of removal of all capillary wave contributions to obtain intrinsic quantities.
Theory of rotational energy levels of open-shell complexes containing the O2 molecule
Authors: Qian Hai-Bo , Low Sarah J. , Seccombe Dominic , Howard Brian J.
Published: July 2002

A new effective Hamiltonian is presented for the analysis of the high-resolution spectra of open-shell van der Waals complexes containing the O2 molecule. The effects of electron spin are included but the complications of nuclear spin and resultant nuclear spin splitting are neglected. The Hamiltonian is composed of the rotational, centrifugal distortion, and spin–spin interaction terms. The resulting energy levels are divided into two well-separated groups and the pattern is a complicated function of θ(the angle that the O2 molecule makes with the principal a axis of the complex)and φ (the azimuthal angle of the O2 out of the plane defined by the a and b axes of the complex). This model has been successfully applied to analyze the high-resolution spectrum of O2–N2O in the region of the N2O monomer ν3 vibrational band, which will be presented in a separate paper.
Coherent two-dimensional Raman scattering: Frequency-domain measurement of the intra- and intermolecular vibrational interactions
Authors: Cho Minhaeng , Okumura Ko , Tanimura Yoshitaka
Published: July 2002

A new experiment of frequency-domain coherent two-dimensional Raman scattering is theoretically proposed. By using three fields whose wave vectors and frequencies are independently controlled, one can measure the nonlinear Raman responses in either gas or condensed phases. The connection to the time-domain femtosecond two-dimensional Raman spectroscopy is completely established. By considering several limiting cases in detail, it is found that from the coherent 2D Raman scattering spectrum one can obtain quantitative information on the anharmonicity, anharmonic mode coupling, and polarizability coupling.
Photodestruction spectroscopy of carbon disulfide cluster anions (CS2)n−, n=1–4: Evidence for the dimer core structure and competitive reactions of the dimer anion
Authors: Maeyama Toshihiko , Oikawa Takanobu , Tsumura Tohru , Mikami Naohiko
Published: July 2002

Photodestruction spectra of carbon disulfide cluster anions, (CS2)n−, n=1–4, have been measured with a time-of-flight mass spectrometer coupled with an optical parametric oscillator. The spectra of all the cluster anions of n⩾2 were found to exhibit a similar absorption band peaking at 1.6–1.8 eV, suggesting that a C2S4− core is involved in the cluster anions. Photon energy dependence of competition between electron detachment and dissociation of the dimer anion was also observed. It was found that there is a reaction channel of the dimer anion producing C2S2− and S2, as well as the ordinary dissociation into CS2− and CS2. The most stable form of the dimer anion was investigated by ab initio calculations at the unrestricted Hartree–Fock/6-31+G* level, showing that the stable form involves covalent C–C and S–S bonds. Reaction mechanisms are discussed on the basis of electronic symmetries of the parent and the fragments.
Theoretical study of the low-lying electronic states of XeO and XeS
Authors: Yamanishi Masato , Hirao Kimihiko , Yamashita Koichi
Published: July 2002

The low-lying electronic states and potential energy curves of XeO and XeS arising from the valence dissociation limits of Xe(1S)+O(3P, D1, and S1) and Xe(1S)+S(3P, D1, and S1) and the ion-pair states that correlate with the manifold of Xe+(2P)+O−(2P) and Xe+(2P)+S−(2P) atomic ion states, respectively, are computed using the complete active space self-consistent field (SCF) followed by multireference single and double configuration interaction methods. The theoretical emission spectra attributed to the ion-pair states of XeO and XeS are reproduced by wave packet propagations and successfully compared to the experimental spectral profile.
Radial and orientational solvation structure of the sodium chloride ion pair in dimethyl sulfoxide
Authors: Das Ashok K. , Tembe B. L.
Published: July 2002

The structures of the solvation shells around each ion of the Na+–Cl− ion pair in liquid dimethyl sulfoxide (DMSO) have been studied in terms of the ion–solvent radial distribution functions (RDFs) and the ion–solvent orientational distribution functions (ODFs) at the three interionic separations of 2.6 Å, 4.9 Å, and 7.2 Å. The solvation shell around the sodium ion consists of only three DMSO molecules at the ion–ion separation of 2.6 Å and this number grows to five DMSO molecules at interionic separation 4.9 Å and beyond. These are in contrast with the octahedral solvation shells around sodium ion in water at all ion–ion separations, where the chloride ion replaces a molecule of water only at a short interionic distance of 2.7 Å. The orientational structure of the solvent around the ion pair has been probed by dividing the DMSO solvent into five spatial regions and analyzing the angular distributions in each region. In the shell near the Na+ ion, the orientation of the sulphur–oxygen vector in DMSO is sharply peaked about 155° away from the sodium–sulphur vector for all the three interionic distances. Similarly, the orientation of the DMSO dipole vector is also sharply peaked about 155° away from the sodium–DMSO center of mass (COM) vector. In the shell near the Cl− ion, the orientation of the sulphur–oxygen vector with respect to the chloride-sulphur vector shows broader peaks in the range 20°–100°. The solvent dipole vector gets oriented in a similar fashion with respect to the chloride–COM vector in this shell. In the regions far from the Na+ and Cl− solvation shells, both the sulphur–oxygen vector and the solvent dipole vector have broad distributions covering all the angles except the parallel and the antiparallel alignments. The angles between the Na+–S–O plane (or the Cl−–S–O plane) and the S–Na+–Cl− plane do not show a preference for any specific inclination, in any of the spatial regions around the ion pair. These broad distributions are indicative of a weaker second shell around the ion pair in DMSO than the second shell found in water and are a consequence of the near absence of hydrogen bonding in DMSO.
Phase transitions in layer structured (C10H21NH3)2SnCl6
Authors: Lee K. W. , Park M. W. , Rhee C. , Lee Cheol Eui , Kang J. K. , Kim K.-W. , Lee K.-S.
Published: July 2002

Phase transitions in the quasi-two-dimensional layer structured (C10H21NH3)2SnCl6, an order–disorder transition and a conformational transition of the hydrocarbon chains, were studied by means of 1H NMR (nuclear magnetic resonance). A newly defined order parameter in the low-temperature phase, the dipolar splitting of the rigid hydrocarbon lineshape component, was shown to represent the order–disorder motion of the hydrocarbon chains, explicitly revealing its three-dimensionality. The conformational transition was marked by a discontinuity in the spin-lattice relaxation rate (1/T1). On the other hand, no obvious anomaly was observed in the spin-lattice relaxation rate at the order–disorder transition at 200 MHz, whereas a weak anomaly was observed at 45 MHz, indicating that the critical dynamics associated with the order–disorder transition is manifest in the low-frequency region of the spectral density.
Description of ligand field splitting in terms of density functional theory: Split levels of the lowest-lying subterms of the 4fn−16s2 (n=3–14) configurations in lanthanide monofluorides LnF (Ln=Pr–Yb)
Authors: Ren J. , Whangbo M.-H. , Dai Dadi , Li Lemin
Published: July 2002

The split levels associated with the lowest-lying subterms of the 4fn−16s2 (n=3–14) configurations of lanthanide monofluorides LnF (Ln=Pr–Yb) were calculated by employing the combined ligand field and density functional theory (CLDT) method recently proposed. The 288 calculated split levels are in excellent agreement with experiment and hence shows that the CLDT method can accurately reproduce the low-lying electronic excited states of lanthanide compounds. To quantitatively describe the low-lying electronic states of a lanthanide compound, therefore, the effective ligand potential must include the Coulomb and exchange-correlation potentials of the compound as well as the pseudopotentials of the ligands.
How do quantum effects change conclusions about heterogeneous cluster behavior based on classical mechanics simulations?
Authors: Chartrand Darryl J. , Le Roy Robert J.
Published: July 2002

Comparisons of classical and quantum Monte Carlo simulation of SF6–(Ar)n and SF6–(Ne)n clusters are used to examine whether certain novel types of behavior seen in classical simulations of SF6–(Ar)n and SF6–(Kr)n persist when quantum effects are taken into account. For mixed clusters formed from Ar (and presumably other heavy partners) quantum effects have little effect on calculated properties, even at very low temperatures, so the cluster-size-dependent preference for solvation vs phase separation and “reverse melting” behavior found in the classical simulations may be expected to occur in many heterogeneous systems. On the other hand, quantum effects substantially lower the melting temperatures of clusters formed with Ne, and (except for a couple of unusually stable stacked isomers) effectively remove the barriers separating the maximally-solvated and phase-separated forms, implying that the latter will normally not exist. Moreover, for (at least) the SF6–(Ne)11 species, when quantum effects are taken into account there is little evidence of solidlike behavior down to the lowest temperatures accessible to our simulation (0.4 K), although classical simulations show a sharp freezing transition at 1.5(±0.1) K. Inclusion of three-body triple–dipole Axilrod–Teller–Muto interactions in the overall potential energy has little effect on either quantum or classical Ne cluster simulations.
Pump-probe spectroscopy of H-bonds as the level-crossing problem
Authors: Burshtein A. I. , Chernobrod B. M. , Sivachenko A. Yu.
Published: July 2002

Saturation of the H-bond absorption spectra by a strong laser field is described as a level-crossing problem with diffusional motion along the reaction coordinate. The stationary populations of the ground and excited vibronic states were found, assuming that the light induced transitions between them occur only at the point of exact resonance and the nonradiative decay of the upper state is uniform. The stationary distributions in both states are also obtained and shown to be Gaussian at slow vibrational relaxation, but essentially distorted when relaxation is faster than diffusion. The absorption spectra of the weak probe light in the frame of two-level and three-level models are calculated, which show either loss or gain in different spectral regions. The existence of bleaching and superabsorption branches in corresponding transmission spectra are confirmed.
Vibrational structure in the carbon 1s ionization of hydrocarbons: Calculation using electronic structure theory and the equivalent-cores approximation
Authors: Thomas T. Darrah , Saethre Leif J. , Sorensen Stacey L. , Svensson Svante
Published: July 2002

A simple ab initio procedure is used to calculate the vibrational structure observed in the carbon 1s ionization of seven hydrocarbons (methane, deuteromethane, ethane, ethene, deuteroethene, ethyne, and deuteroethyne), with good agreement between experiment and theory. The method involves use of the equivalent-cores approximation, localized holes in molecules with equivalent carbons, and the harmonic oscillator approximation. The approach provides insight into the vibrational modes of the core-ionized molecules. It is potentially useful in extracting carbon 1s ionization energies from spectra from molecules having inequivalent carbons or in finding information on inner-hole lifetimes from inner-shell spectra.
Chemistry of PO−, PO2−, and PO3− in the gas phase
Authors: Morris Robert A. , Viggiano A. A.
Published: July 2002

Rate constants have been measured for reactions of the small oxyphosphorus anions PO−, PO2−, and PO3− with a selection of reactant neutrals at 300 K using a selected ion flow tube instrument. The PO− anion was the most reactive, abstracting an oxygen atom from O2, NO, CO2, and NO2 with rates below collisional. Of the neutrals studied, only NO2 transferred an O atom to PO2−, demonstrating that NO2 can provide a route from PO− to PO3− through PO2−. PO2− was found to react with WF6 through fast charge transfer, and with H2O by slow clustering. The only observed reaction found for the highly stable PO3− anion was slow clustering with H2O.
Ultrahigh-resolution spectroscopy of the A1Au←X1Ag transition of trans-glyoxal
Authors: Katô Hajime , Sawa Katsuhiro , Kuwano Hiroyuki , Kasahara Shunji , Baba Masaaki , Nagakura Saburo
Published: July 2002

Doppler-free two-photon absorption spectra of the A1Au(v7=1)←X1Ag(v=0) transition of trans-glyoxal and the effects of magnetic fields up to 14 kG are measured. The absolute energies of transition lines are measured with accuracy better than 0.000 03 cm−1, and T0 is determined to be 22 206.749 43 cm−1. From the analysis of the perturbed A1Au and perturbing a3Au levels, the hyperfine constant of the deperturbed a3Au level is determined to be 88 MHz. The magnetic moment of the a3Au level is determined to be 0.86μB from the magnitude of Zeeman splitting of a hyperfine component. From an analysis of the Zeeman splittings of unperturbed levels, which are transitions to the A1Au state and where no appreciable energy shifts are observed, the 13Bu state is shown to be slightly mixed into the 11Au state: |A1Au〉≃|11Au〉+0.02|13Bu〉. The perturbation between the A1Au(v7=1(au)) and a3Au(v′(au)) levels is shown to occur through the vibronic interaction between the mixed 13Bu(v″(au)) and the a3Au(v′(au)) states. The perturbation is appreciable if levels of the A1Au and a3Au states are accidentally close in energy. The energy spacing between levels of the A1Au and a3Au states changes with the magnetic field, and the resulting changes of the perturbation are observed. The mechanism of the intersystem crossing of a chosen single level A1Au(v7=1(au),K,J) is clarified in this study.
Theoretical study of the reactions of Ar++H2 and Ar++HD using the trajectory surface hopping method
Authors: Sizun Muriel , Song Ju-Beom , Gislason Eric A.
Published: July 2002

Trajectory surface hopping calculations have been carried out for collisions of Ar++H2 and Ar++HD on three low-lying potential energy surfaces projected from the original six in the Kuntz and Roach diatomics in molecules surface for this system. The location and probability of hops between surfaces were determined using the new algorithm developed by Parlant and Gislason. In addition to the reactive channel and total charge transfer to H2+ and HD+, dissociative channels to, for example, Ar++H+H, and Ar+H++H have been studied. Particular attention was paid to the dissociative charge transfer isotope effect for the processes Ar++HD→Ar+H++D, or Ar+H+D+; near threshold the D+ product is favored over H+ which we attribute to preferential dissociation of excited ArD+ products. This is the first theoretical study of these dissociation processes.
Internal rotation and Stark effect in CH3SiD3
Authors: Ozier Irving , Meerts W. Leo
Published: July 2002

The avoided-crossing molecular-beam method has been applied to CH3SiD3 in the ground torsional state (υ6=0). Three “rotational” anticrossings have been measured corresponding to normally forbidden transitions in which both the rotational and leading torsional energy terms change. Each torsional sublevel with (J=4,k=∓1) and given torsion–rotation symmetry Γ undergoes an avoided crossing with its counterpart with (J=3,k=±2) and the same Γ. Four “barrier” anticrossings have been measured corresponding again to normally forbidden transitions, but in which only the torsional energy changes. These transitions are (J↔J), (k=±1↔∓1), and (Γ=E3↔E2,E1) for J=1 and 2. From these seven zero-field splittings and nine existing R-branch microwave frequencies for υ6⩽2, nine torsion–rotation parameters have been determined including the effective rotational constant Aeff=34 192.04(11) MHz and the effective height of the barrier to internal rotation V3eff=585.08(5) cm−1. For each anticrossing studied, an estimate has been made of the contribution δνhyp to the zero-field splitting from the nuclear hyperfine interactions. For CH3SiH3, CH3CD3, and CH3SiF3, barrier anticrossings have been previously investigated. For each of these anticrossings, estimates of δνhyp are made here as well. For all cases studied (including those for CH3SiD3), it is found that |δνhyp|≲5 kHz. For CH3SiD3, by using conventional electric-resonance molecular-beam methods, the electric dipole moment has been determined to an accuracy of ∼55 ppm for each of the rotational states (J,k)=(1,±1), (2,±1), and (3,±2).
A displaced and low-frequency vibration of phosphorescent state of trans-[Rh(ethylenediamine)2Cl2]PF6 in a range of 5–497 K
Authors: Islam Ashraful , Ikeda Noriaki , Nozaki Koichi , Ohno Takeshi
Published: July 2002

The lowest (dπ-dσ*)3 excited states of both cis- and trans-isomers of [Rh(en)2Cl2]X (en=ethylenediamine; X=PF6−, NO3−) and the deuteriated crystal of trans-[Rh(en-d4)2Cl2]PF6 have been investigated in the solid state and in a wide temperature range of 5–497 K by means of emission spectra, lifetime and quantum yield measurements. Emission spectral simulation of trans-[Rh(en)2Cl2]PF6 shows that the emission from the lowest (dπ-dσ*)3 excited state exhibits a progression of a low-frequency metal-chloride stretching vibration (250 cm−1) with a large Huang-Rhys factor (S) of 21 and a progression of a high-frequency N–H stretching vibration (3000 cm−1). The increasing full-width at half maximum (2200 cm−1→4400 cm−1) with increasing temperature (77 K→468 K) is ascribed to hot bands from the excited levels of low-frequency vibration. The luminescence quantum yields of the crystal samples are determined to 0.0008 at 298 K and 0.003 at 80 K for trans-[Rh(en)2Cl2]PF6 and 0.18 at 298 K and 0.40 at 80 K for trans-[Rh(en-d4)2Cl2]PF6. From a combination of lifetime and emission quantum yield measurements, values for kr and knr have been obtained. The observed temperature dependence of nonradiative decay rates of trans-[Rh(en-d4)2Cl2]PF6 in a low-temperature region (<300 K) is possible to reconstitute by using the emission spectral fitting parameters and assuming nuclear tunneling mechanism. The temperature effect and deuteriation effect on the nonradiative rate definitively establishes that the dominant “accepting” modes in the nonradiative transition are a highly displaced (S=21) vibrational mode of low-frequency Cl–Rh–Cl stretching and a weakly displaced (S=0.1) vibrational mode of high-frequency N–D stretching. The nonradiative transition in a high-temperature region occurs via barrier passing along a displaced coordinate of Cl–Rh–Cl vibration with a pre-exponential factor of 1011 s−1 and is relatively insensitive to the high-frequency vibrational mode. The crystal of cis-[Rh(en)2Cl2]NO3 shows a red shift of the emission peak energy and an increase in the full-width at half maximum with increasing temperature. The results of temperature-dependent decay and spectra of emission can be interpreted in terms of two (dπ-dσ*)3 emitting states model.