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22 Sep 2001

Volume 115, Issue 12, pp. 5345-5694

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Predissociation dynamics of formyloxyl radical studied by the dissociative photodetachment of HCO2−/DCO2−+hν→H/D+CO2+e−

Todd G. Clements and Robert E. Continetti

J. Chem. Phys. 115, 5345 (2001); http://dx.doi.org/10.1063/1.1404143 (4 pages) | Cited 12 times

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The dissociative photodetachment (DPD) of HCO2− and DCO2− was studied at 258 nm. State-resolved translational energy distributions were observed correlated to bending excitation in the CO2 product for the channel producing H/D+CO2, indicating very low rotational excitation in the products consistent with predissociation of a C2ν HCO2 molecule. No evidence was found for dissociation into OH+CO. All three low-lying electronic states (2A1, 2B2, and 2A2) were found to dissociate, but resolved progressions were only observed from photodetachment to the 2A1 and 2B2 states. Photoelectron-photofragment coincidence spectra for DCO2− show resolved vertical bands and indicate that multiple CO2 vibrational states are accessible from each vibrational level in the predissociating DCO2 molecule. The resolved structure is assigned to vibrational predissociation sequence bands, observable in this DPD process owing to the dissociation dynamics and the near degeneracy of the vibrational levels in the 2A1 and 2B2 states of HCO2 and the bending mode of the CO2 products. © 2001 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants

Theory of enantiomeric control in dimethylallene using achiral light

David Gerbasi, Moshe Shapiro, and Paul Brumer

J. Chem. Phys. 115, 5349 (2001); http://dx.doi.org/10.1063/1.1405116 (4 pages) | Cited 21 times

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Extensive control over enantiomer populations using achiral light is computationally demonstrated for J, MJ-selected 1,3 dimethylallene. In particular, by altering the detuning of one of three lasers incident on an J, MJ-polarized racemic mixture, one can alter the enantiomeric excess from ≈93% of the L enantiomer to ≈93% of the D enantiomer. © 2001 American Institute of Physics.
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33.80.-b Photon interactions with molecules
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
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back to top Theoretical Methods and Algorithms

Path integral molecular dynamics method based on a pair density matrix approximation: An algorithm for distinguishable and identical particle systems

Shinichi Miura and Susumu Okazaki

J. Chem. Phys. 115, 5353 (2001); http://dx.doi.org/10.1063/1.1397328 (9 pages) | Cited 9 times

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In this paper, the path integral molecular dynamics (PIMD) method has been extended to employ an efficient approximation of the path action referred to as the pair density matrix approximation. Configurations of the isomorphic classical systems were dynamically sampled by introducing fictitious momenta as in the PIMD based on the standard primitive approximation. The indistinguishability of the particles was handled by a pseudopotential of particle permutation that is an extension of our previous one [J. Chem. Phys. 112, 10 116 (2000)]. As a test of our methodology for Boltzmann statistics, calculations have been performed for liquid helium-4 at 4 K. We found that the PIMD with the pair density matrix approximation dramatically reduced the computational cost to obtain the structural as well as dynamical (using the centroid molecular dynamics approximation) properties at the same level of accuracy as that with the primitive approximation. With respect to the identical particles, we performed the calculation of a bosonic triatomic cluster. Unlike the primitive approximation, the pseudopotential scheme based on the pair density matrix approximation described well the bosonic correlation among the interacting atoms. Convergence with a small number of discretization of the path achieved by this approximation enables us to construct a method of avoiding the problem of the vanishing pseudopotential encountered in the calculations by the primitive approximation. © 2001 American Institute of Physics.
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71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.20.Ja Computer simulation of liquid structure

On the accuracy of the fixed-node diffusion quantum Monte Carlo method

Sebastian Manten and Arne Lüchow

J. Chem. Phys. 115, 5362 (2001); http://dx.doi.org/10.1063/1.1394757 (5 pages) | Cited 40 times

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The accuracy of the fixed-node diffusion quantum Monte Carlo (FN-DQMC) method is compared to the coupled cluster method CCSD(T). For a test set of 20 small molecules and 17 reactions the electronic contribution to the reaction enthalpy is calculated with the FN-DQMC method using the nodes of a Slater determinant calculated at the HF/cc-pVTZ level. By comparison with reference reaction enthalpies the FN-DQMC method is shown to be more accurate than the CCSD(T)/cc-pVDZ method and almost as accurate as CCSD(T)/cc-pVTZ. The deviation from the reference data is comparable to the CCSD(T)/cc-pVTZ deviation, but, with only two exceptions, of opposite sign. © 2001 American Institute of Physics.
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31.15.bw Coupled-cluster theory
82.60.Cx Enthalpies of combustion, reaction, and formation

Multidimensional quantum propagation with the help of coupled coherent states

Dmitrii V. Shalashilin and Mark S. Child

J. Chem. Phys. 115, 5367 (2001); http://dx.doi.org/10.1063/1.1394939 (9 pages) | Cited 48 times

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A previous initial value coupled coherent state (CCS) representation is applied to Gaussian wave packet propagation on multidimensional Henon Heiles potentials. Solutions of the time-dependent integro-differential Schrödinger equation are obtained in a basis of trajectory guided Frozen Gaussian Coherent States, with Monte Carlo sampling to ensure a unique capability for propagating multidimensional wave functions. Results, which are obtained for up to 14 D, are compared with those derived by the Herman–Kluk semiclassical initial value representation (IVR) wave packet method. © 2001 American Institute of Physics.
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03.65.Ge Solutions of wave equations: bound states
02.30.-f Function theory, analysis

Trapping of Brownian particles by random spheres of different radii

Alexander M. Berezhkovskii, Yurii A. Makhnovskii, and George H. Weiss

J. Chem. Phys. 115, 5376 (2001); http://dx.doi.org/10.1063/1.1396673 (5 pages) | Cited 3 times

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We analyze the survival of a Brownian particle moving among randomly distributed spherical traps of two different radii. All of the results known in the case of identical traps, the mean-field Smoluchowski solution, the lowest order correction of this solution, the cumulant expansion, and the long-time behavior, are generalized to the case of two types of traps. Our approach is readily extended to deal with trapping spheres having more than two different radii. © 2001 American Institute of Physics.
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05.40.Jc Brownian motion

Linear and nonlinear response functions of the Morse oscillator: Classical divergence and the uncertainty principle

Jianlan Wu and Jianshu Cao

J. Chem. Phys. 115, 5381 (2001); http://dx.doi.org/10.1063/1.1389840 (11 pages) | Cited 29 times

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The algebraic structure of the quantum Morse oscillator is explored to formulate the coherent state, the phase-space representations of the annihilation and creation operators, and their classical limits. The formulation allows us to calculate the linear and nonlinear quantum response functions for microcanonical Morse systems and to demonstrate the linear divergence in the corresponding classical response function. On the basis of the uncertainty principle, the classical divergence is removed by phase-space averaging around the microcanonical energy surface. For the Morse oscillator, the classical response function averaged over quantized phase space agrees exactly with the quantum response function for a given eigenstate. Thus, phase-space averaging and quantization provide a useful way to establish the classical-quantum correspondence of anharmonic systems. © 2001 American Institute of Physics.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
03.65.-w Quantum mechanics

Thermohydrodynamics for a van der Waals fluid

Pep Español

J. Chem. Phys. 115, 5392 (2001); http://dx.doi.org/10.1063/1.1394212 (12 pages) | Cited 13 times

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Following a cell method of van Kampen for the calculation of a coarse-grained free-energy functional for the van der Waals gas, we compute a corresponding entropy functional from microscopic principles. This entropy functional is one of the building blocks of the recently developed GENERIC framework [H. C. Öttinger and M. Grmela, Phys. Rev. E 56, 6633 (1997)]. This framework allows us to obtain, in a thermodynamically consistent way, the continuum hydrodynamic equations for a fluid able to display liquid–vapor coexistence. Surface tension appears naturally and the resulting model describes interfaces as diffuse regions, much in the same spirit as the gradient theory for equilibrium situations. We suggest that using interfacial forces in the integral form obtained in the microscopic derivation instead of third order derivatives of the density field might represent an advantage from a computational point of view. © 2001 American Institute of Physics.
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51.30.+i Thermodynamic properties, equations of state
65.20.-w Thermal properties of liquids
64.70.F- Liquid-vapor transitions
68.03.Cd Surface tension and related phenomena
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Photoelectron spectroscopy of bimetallic aluminum cobalt cluster anions: Comparison of electronic structure and hydrogen chemisorption rates

Axel Pramann, Atsushi Nakajima, and Koji Kaya

J. Chem. Phys. 115, 5404 (2001); http://dx.doi.org/10.1063/1.1394944 (7 pages) | Cited 10 times

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The photoelectron spectra of small mass-selected aluminum-rich AlnCo− (n = 8–17) and cobalt-rich ConAlm− clusters (n = 6,8,10; m = 1,2) are measured at photon energies of 3.49 eV with the aid of a magnetic bottle photoelectron spectrometer. The electronic structures of the bimetallic clusters are compared with those of pure Aln− and Con− clusters, which are measured under the same conditions. The threshold behavior (electron affinities and vertical detachment energies) is analyzed, and the application of the electronic shell model reveals a similar shell structure of Co-doped Al clusters with a single heteroatom. Additional heteroatom doping induces shell perturbations. Compared to pure Aln clusters, single-atom doped clusters show a hybridization of Al s, p and Co d orbitals resulting in a merging of spectral features at low binding energies. The evolution of the electronic structure is compared with reported ionization potentials [Menezes and Knickelbein, Chem. Phys. Lett. 183, 357 (1991); Z. Phys. D 26, 322 (1993)]. The hydrogen chemisorption behavior of neutral aluminum cobalt clusters [Nonose et al., Chem. Phys. Lett. 164, 427 (1989)] shows a clear influence of Co d states at low binding energies in the case of AlnCo, whereas for ConAlm clusters (n>m) the geometric effect becomes more dominant. © 2001 American Institute of Physics.
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33.60.+q Photoelectron spectra
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters

Ab initio studies of dissociation pathways on the ground- and excited-state potential energy surfaces for HFCO

Wei-Hai Fang and Ruo-Zhuang Liu

J. Chem. Phys. 115, 5411 (2001); http://dx.doi.org/10.1063/1.1398096 (7 pages) | Cited 6 times

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Potential energy surfaces of the HFCO dissociation to H+FCO and F+HCO in the lowest three electronic states (S0, S1, and T1) have been investigated with ab initio molecular orbital method at the level of the complete active space self-consistent field. An insight into the dynamics of the HFCO photodissociation at the range of 193–248 nm was provided in the present work. Radiationless transfer from S1 to T1 and subsequent dissociation on the T1 surface was predicted to be the mechanism for the C–H bond cleavage, which is consistent with that proposed by experimentalists. The experimental investigations of the HFCO photodissociation suggest that the F–C bond fission also occurs as a result of intersystem crossing (ISC) from S1 to T1, which is not supported by the present calculations. This has been discussed in detail. © 2001 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.37.Vb Single molecule photochemistry
82.50.Hp Processes caused by visible and UV light
82.20.Kh Potential energy surfaces for chemical reactions
33.50.Hv Radiationless transitions, quenching

High resolution femtosecond coherent anti-Stokes Raman scattering: Determination of rotational constants, molecular anharmonicity, collisional line shifts, and temperature

T. Lang, M. Motzkus, H. M. Frey, and P. Beaud

J. Chem. Phys. 115, 5418 (2001); http://dx.doi.org/10.1063/1.1397325 (9 pages) | Cited 41 times

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In this paper we present high resolution spectroscopy performed with femtosecond coherent anti-Stokes Raman scattering (CARS). After a theoretical treatment of the issue, specific experimental configurations will be introduced. Transients from nonresonant rotational and vibrational CARS on di- and polyatomics in the gas phase were analyzed. Rotational and vibrational constants and pressure-dependent line shifts are determined with high accuracy. The method is suitable for precise measurement of temperatures. We present thermometry on combustion relevant species like H2 and N2 and discuss the reliability and accuracy of the data. © 2001 American Institute of Physics.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts
33.15.Mt Rotation, vibration, and vibration-rotation constants

The HD–He complex: Interaction-induced dipole surface and infrared absorption spectra

Magnus Gustafsson and Lothar Frommhold

J. Chem. Phys. 115, 5427 (2001); http://dx.doi.org/10.1063/1.1396851 (6 pages) | Cited 6 times

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The collision-induced dipole surface of an HD molecule interacting with an He atom is derived from the ab initio dipole data of the H2–He complex [Gustafsson et al., J. Chem. Phys. 113, 3641, (2000)]. Collision-induced absorption spectra of gaseous mixtures of deuterium hydride and helium in the rotational and fundamental bands of HD are calculated, for comparison with an existing measurement taken at a temperature of 77 K. To that end, we integrate the close-coupled, radial Schrödinger equations, accounting for the anisotropy of the HD–He interaction potential. The computed absorption spectra generally agree reasonably well with the observed spectral profiles and intensities of the collision-induced spectra. We also consider the interference phenomena of the HD permanent dipole with the interaction-induced, supramolecular dipole by computing the wings of various R(j) lines and of the P1(1) line in single, binary collision limit. For comparison, the line broadening and shift for the P and R line shape parameters are also computed using the impact approximation. The close-coupled treatment of our calculation of the spectral profiles accounts for rotational level mixing in a nonperturbative manner. The treatment is fully quantum-mechanical and takes into account single binary collisions of HD and He. © 2001 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.70.Jg Line and band widths, shapes, and shifts
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.20.Ea Infrared spectra
31.15.A- Ab initio calculations

Experimental and theoretical studies of the near-infrared spectrum of bromomethylene

Hua-Gen Yu, Tomas Gonzalez-Lezana, Andrew J. Marr, James T. Muckerman, and Trevor J. Sears

J. Chem. Phys. 115, 5433 (2001); http://dx.doi.org/10.1063/1.1386812 (12 pages) | Cited 18 times

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New measurements in the  1A″–math 1A′ band system of monobromomethylene (HCBr) at near-infrared wavelengths are reported. Rotationally resolved spectra of HCBr and DCBr for both naturally occurring Br isotopes are analyzed and provide accurate energies for the low-lying bending vibrational levels in both the and math states. The experimental results are compared to extensive ab initio calculations of these two states and the low-lying  3A″ state. The ab initio T00 value for the –math system is calculated within 500 cm−1 of the experimental results. For the triplet state, T00 (math–math) was calculated to be 1833 cm−1. The measurements of the bending intervals in the math 1A′ state suggest that this is about 250 cm−1 too low. With this shift and inclusion of spin–orbit coupling between the and math states, the calculated bending vibrational levels in the math state reproduce the observations, and the calculations make testable predictions of the position of the triplet and other singlet state vibronic levels. Combining the experimental and computational results, we estimate the triplet, T00(–math), excitation energy to be 2028 cm−1. © 2001 American Institute of Physics.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Anharmonic vibrational frequencies of proton transfer coordinates in the clusters of aromatic molecules with water

A. Jansen and M. Gerhards

J. Chem. Phys. 115, 5445 (2001); http://dx.doi.org/10.1063/1.1394753 (9 pages) | Cited 12 times

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The vibrational frequencies of OH and NH groups which form hydrogen bonds to a water molecule are calculated using the complete active space self-consistent field (CASSCF) method and the second order perturbation theory based on the CASSCF reference (CASPT2). As model systems indole(H2O), phenol(H2O), and their corresponding cations are chosen. Furthermore, different isomers of the 3-aminophenol(H2O)+ and 4-aminophenol(H2O)+ clusters are considered. For all these clusters IR spectra are known, but the IR spectra of the ionic clusters in the region of the hydrogen-bonded OH and NH groups have not yet been well interpreted. Due to the strong anharmonicity of the OH and NH vibrations it is not possible to predict their frequencies by a simple scaling of harmonic values. By using different active spaces including both π-orbitals as well as σ-orbitals it is shown that the vibrational frequencies can be derived from potentials obtained from CASSCF single-point calculations along the OH and NH stretching modes. These vibrations can be regarded as proton-transfer coordinates. The calculated vibrational frequencies are in excellent agreement with the experimental values obtained for the investigated clusters. Furthermore, a strong shift of the OH stretching frequency is predicted by going from phenol(H2O)+ to aminophenol(H2O)+ clusters, explaining the completely different IR spectra of the investigated species. © 2001 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Wa Charged clusters
36.40.Sx Diffusion and dynamics of clusters
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
33.15.Fm Bond strengths, dissociation energies
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
33.20.Ea Infrared spectra
33.70.Jg Line and band widths, shapes, and shifts

Anisotropic photodissociation of CH3Cl+•

Dong Shin Won, Myung Soo Kim, Joong Chul Choe, and Tae-Kyu Ha

J. Chem. Phys. 115, 5454 (2001); http://dx.doi.org/10.1063/1.1397326 (7 pages) | Cited 9 times

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Photodissociation of the methyl chloride ion has been investigated using mass-analyzed ion kinetic spectrometry (MIKES). The MIKE spectrum for the chlorine atom loss from the methyl chloride ion has been measured as a function of the laser polarization angle at 357, 488.0, and 514.5 nm. The anisotropy parameters and kinetic energy release distributions have been determined. At all the wavelengths used, an anisotropic dissociation (β = 1.2) in the repulsive excited electronic state has been observed. Results from quantum chemical calculations carried out at the various levels suggest that the methyl chloride ion is excited to the first excited electronic state , and dissociates repulsively in this state. © 2001 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.37.Vb Single molecule photochemistry
82.50.Hp Processes caused by visible and UV light

Selective field ionization of high Rydberg states: Application to zero-kinetic-energy photoelectron spectroscopy

U. Hollenstein, R. Seiler, H. Schmutz, M. Andrist, and F. Merkt

J. Chem. Phys. 115, 5461 (2001); http://dx.doi.org/10.1063/1.1396856 (9 pages) | Cited 38 times

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Sequences of pulsed electric fields have been designed and tested that enable a higher selectivity in the pulsed field ionization of high Rydberg states (n ≥ 100) than has so far been possible. The enhanced selectivity originates from the permutation of the parabolic quantum numbers n1 and n2 that is induced by a sufficiently rapid inversion of the electric field polarity during a pulse sequence. A reliable procedure, based on numerical simulations of the outcome of pulse field ionization sequences, has been developed to detect and control changes in the parabolic quantum numbers that can occur during a pulse sequence. The procedure can be used to assess under which conditions a clean permutation of the parabolic quantum numbers can be achieved. Unwanted randomization of m, n1 and n2, which reduces the selectivity of the field ionization process, can be avoided by minimizing the time intervals during which the electric field in the pulse sequence is almost zero. The high selectivity reached in the pulsed field ionization of high Rydberg states has been used to record pulsed-field-ionization zero-kinetic-energy photoelectron spectra of argon and nitrogen at an unprecedented resolution of 0.06 cm−1. This resolution opens new perspectives in photoelectron spectroscopy. © 2001 American Institute of Physics.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
34.50.Gb Electronic excitation and ionization of molecules
33.60.+q Photoelectron spectra
32.80.Fb Photoionization of atoms and ions

Thermodynamic investigation of the Si7 and Si8 clusters by Knudsen cell mass spectrometry

G. Meloni and K. A. Gingerich

J. Chem. Phys. 115, 5470 (2001); http://dx.doi.org/10.1063/1.1391265 (7 pages) | Cited 9 times

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The Knudsen cell mass spectrometric method has been employed to measure the partial pressures of the Si7 and Si8 clusters under equilibrium conditions above liquid silicon, contained in a boron nitride liner inside a graphite Knudsen cell. Gaussian 2 (G2) theory and B3LYP density functional method were employed to determine the geometry, the vibrational frequencies, and the binding energy of the Si8 cluster. From the all-gas analyzed equilibria the following atomization enthalpies, ΔaH0o(Sin), and enthalpies of formation, ΔfH298.15o(Sin), in kJ mol−1, have been obtained: Si7, 2381±36 and 743±36; Si8, 2735±65 and 837±65. Experimental literature values for the electron affinities of Sin(n = 3–8) have been combined with present and previous results to obtain the bonding energies for the Sin−(n = 3–8) cluster anions. The experimental atomization energies are compared with available theoretical values. © 2001 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
82.60.Cx Enthalpies of combustion, reaction, and formation
33.15.Ta Mass spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

Full-dimensional quantum study of the vibrational predissociation of the I2⋯Ne2 cluster

C. Meier and U. Manthe

J. Chem. Phys. 115, 5477 (2001); http://dx.doi.org/10.1063/1.1389307 (8 pages) | Cited 20 times

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The dynamics of the vibrational predissociation of the I2Ne2(B,ν = 21) cluster is studied using a full-dimensional time-dependent wave packet approach. The 6-D propagation is performed with the multiconfiguration time-dependent Hartree (MCTDH) method. The time dependence of the I2 vibrational state populations is monitored during the dissociation process. The final vibrational populations are compared to experimental findings of Levy et al. © 2001 American Institute of Physics.
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36.40.Cg Electronic and magnetic properties of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods

Emission spectroscopy, harmonic vibrational frequencies, and improved ground state structures of jet-cooled monochloro- and monobromosilylene (HSiCl and HSiBr)

David A. Hostutler, Nicholas Ndiege, Dennis J. Clouthier, and Steven W. Pauls

J. Chem. Phys. 115, 5485 (2001); http://dx.doi.org/10.1063/1.1397795 (7 pages) | Cited 11 times

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The ground state harmonic frequencies of gas phase H/DSi35Cl and H/DSi79Br have been determined by exciting single vibronic bands of the  1A″–math 1A′ electronic transition and recording the dispersed fluorescence. The jet-cooled radicals were produced in a pulsed discharge jet using H/DSiX3 (X=Cl or Br) precursors. The emission data were fitted to an anharmonic model and a normal coordinate analysis of the harmonic frequencies allowed the determination of five of the six force constants of each molecule. Using previously obtained v″ = 0 rotational constants and the improved force fields, average (rz) and estimated equilibrium (rez) structures were calculated for both monohalosilylenes. The validity of the force constants was evaluated by comparing calculated and observed zero-point inertial defects and by simulating the Franck–Condon profiles of the observed emission spectra in the harmonic approximation. © 2001 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Sn Rotational analysis

Numerical simulations of molecular orientation using strong, nonresonant, two-color laser fields

Tsuneto Kanai and Hirofumi Sakai

J. Chem. Phys. 115, 5492 (2001); http://dx.doi.org/10.1063/1.1398311 (6 pages)

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We have investigated the possibility of molecular orientation using an asymmetric potential created by the superposition of strong, nonresonant, two-color (ω+2ω) laser fields. The time-independent Schrödinger equations are solved numerically for FCN molecules as an example in an adiabatic regime where the orientation proceeds slowly compared to the rotational period of molecules. We show the laser intensity dependence of the orientation parameter cos θ and the alignment parameter cos2 θ where θ is the angle between the polarization axis and the molecular axis, and their time evolution during the laser fields, suggesting that our approach can be used to orient polar molecules if they are rotationally cold. © 2001 American Institute of Physics.
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37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
42.50.-p Quantum optics

The 19F–1H coupling constants transmitted through covalent, hydrogen bond, and van der Waals interactions

Magdalena Pecul, Joanna Sadlej, and Jerzy Leszczynski

J. Chem. Phys. 115, 5498 (2001); http://dx.doi.org/10.1063/1.1398099 (9 pages) | Cited 15 times

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The 19F–1H coupling constants were calculated on the multiconfiguration self-consistent field (MCSCF) level in several systems, ranging from covalently bonded HF, hydrogen bonded FHF− and (HF)2 complexes to weak van der Waals complex CH4–HF. The sign of the 19F–1H coupling varies in this sequence, and its absolute value decreases. Still, it is sizable even for CH4–HF. The distance dependence of 19F–1H coupling is essentially the same in all systems under study, and the calculations for FHF− with distorted geometry suggest that the value of 19F–1H coupling is determined mainly by molecular geometry. 19F–19F coupling constants were also analyzed. 19F–19F intermolecular coupling in (HF)2 is substantial but has the opposite sign to that in FHF− and its counterpart in (H2O)2. © 2001 American Institute of Physics.
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33.25.+k Nuclear resonance and relaxation
31.15.xr Self-consistent-field methods
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies

Production of ground state OH following electron impact on H2O

T. Harb, W. Kedzierski, and J. W. McConkey

J. Chem. Phys. 115, 5507 (2001); http://dx.doi.org/10.1063/1.1397327 (6 pages) | Cited 22 times

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Laser-induced fluorescence (LIF) measurements of OH(X 2Π) production following electron impact on water have been carried out over an energy range from threshold to 300 eV. Data have been made absolute using existing measurements of OH(X) production via dissociative attachment. The cross section reaches a maximum value of 2.1×10−16 cm2 at an energy of 75 eV. Dipole-allowed processes are shown to dominate the production of OH(X) particularly via the A(1B1) repulsive state, though significant population of higher rotational levels is demonstrated, indicating the relevance of other channels as in photodissociation. © 2001 American Institute of Physics.
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34.80.Ht Dissociation and dissociative attachment
33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Heterogeneous relaxation in supercooled liquids: A density functional theory analysis

Rajesh K. Murarka and Biman Bagchi

J. Chem. Phys. 115, 5513 (2001); http://dx.doi.org/10.1063/1.1396849 (8 pages) | Cited 2 times

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Recent time domain experiments which allow selective study of the relaxation of slower subpopulations among the distributions of local, inhomogeneous regions, have shown the existence of a length scale (∼2–3 nm) beyond which the liquid behaves like a homogeneous liquid. Here we use the density functional theory to calculate the probability of creating a soft localized density fluctuation (density droplet). Theoretical calculation shows that the free energy penalty for creating a local inhomogeneity of small size is much less than that for a large size and that a dense supercooled system is unlikely to sustain inhomogeneity of a length, lf, which is larger than 5σ, where σ is the molecular diameter. We have calculated both the equilibrium and the nonequilibrium (subsequent to photobleaching) orientational correlation functions with the theoretically obtained inhomogeneous distributions. The nonequilibrium distribution relaxes at a slower rate. A simple two state exchange model has been used to mimic the relaxation of the slow regions to equilibrium; the model shows that the diffusional exchange cannot be the mechanism for the extremely slow relaxation process very near to the glass transition temperature. These results have been compared with recent experimental results. © 2001 American Institute of Physics.
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61.20.Gy Theory and models of liquid structure

A comparison of the properties of 2,2,2-trifluoroethanol and 2,2,2-trifluoroethanol/water mixtures using different force fields

Rajappa Chitra and Paul E. Smith

J. Chem. Phys. 115, 5521 (2001); http://dx.doi.org/10.1063/1.1396676 (10 pages) | Cited 25 times

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It is necessary to evaluate the quality of a force field by comparison with known experimental properties before it can be used with confidence in a simulation. Here, such a study is reported for pure 2,2,2-trifluoroethanol (TFE) solutions and for TFE/water mixtures at two different compositions. Six literature force fields were examined using molecular dynamics simulations. It is found that none of the currently available force fields describe all the properties of pure liquid TFE. The models of van Buren and Berendsen, Duffy and Jorgensen, and Fioroni et al. produce properties that are in reasonable agreement with experiment. The ability to adequately describe properties of TFE/water mixtures varied with the property of interest. The heat of mixing is too unfavorable for all the models. The aggregation properties of the mixtures were well described by the model of Duffy and Jorgensen at the lower composition (30% by volume of TFE), while the Fioroni et al. model performed better at higher TFE concentrations. The activity coefficient derivative from the Fioroni et al. model was in very good agreement with experiment for all compositions studied here. Consequently, the choice of the most appropriate force field will depend on the major properties of interest. © 2001 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
64.75.-g Phase equilibria

Electronic and vibrational dynamic solvent effects on Raman spectra

Chiara Cappelli, Stefano Corni, and Jacopo Tomasi

J. Chem. Phys. 115, 5531 (2001); http://dx.doi.org/10.1063/1.1396678 (5 pages) | Cited 10 times

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We report a methodology for the theoretical evaluation of nonequilibrium solvent effects on Raman intensities within the nonequilibrium Polarizable Continuum Model. Effects due to an incomplete solvent response both to the external field-induced oscillation in the solute electronic density and to molecular vibrations are considered. The extent of such effects on absolute scattering factors and relative intensities of few simple molecules (HCHO, FCHO, FCFO, ClCHO, ClCClO) in various solvents are discussed. © 2001 American Institute of Physics.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Mt Rotation, vibration, and vibration-rotation constants
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