bluuebunny/crossref_metadata_2025 huggingface dataset:
High-energy overtone spectroscopy of some deuterated methanes
Authors: Perry J. W. , Moll D. J. , Kuppermann A. , Zewail A. H.
Published: July 2002

High-energy overtone photoacoustic spectroscopy of gas phase CHD3 (ΔvCH=5,6, and 7), CH2D2, CH3D, and CH4 (ΔvCH=6) is reported. The overtone and combination bands of CHD3 display partially resolved rotational structure with laser limited linewidths (∼0.5 cm−1). A combination sum analysis is used to generate excited state rotational constants B′. We present an analysis of the Fermi resonances of CHD3 which indicates strong interactions of the CH stretch with degenerate bending modes. The relative intensities of the Fermi interacting states are in agreement with those calculated from an analysis based on frequency shifts and a two or three level model. However, the rotational B′ constants are not explained by such simple models indicating further interactions with states as yet unobserved. An upper limit of 10 cm−1 is estimated for the splitting of the ‖6,0〉± local mode states for CH2D2, giving support to a description based on the local mode picture. For CH3D and CH4 the spectra are apparently congested by overlapping overtone and combination bands and perhaps other mechanisms not identified in this work. Generally, our results emphasize the importance of the interactions of CH stretching with CH bending motions.
Second-order electron correlation energies for some 3d1 and 3d14s2 ions
Authors: Jankowski K. , Malinowski P. , Polasik M.
Published: July 2002

Second-order correlation energies for the ground states of Cu−, Ge2+, Kr6+ (3d104s2 configuration) and Cu+ and Kr8+ (3d10 configuration) are calculated within the framework of the variational-perturbation formulation of the Rayleigh–Schrödinger Hartree–Fock perturbation theory. The method is based on the application of symmetry-adapted pair functions taken in the form of partial-wave (PW) expansions. M- and N-intrashell as well as LM- and MN-intershell correlation effects were considered. Special attention is paid to the determination of the Z-dependence of both the PW increments to the pair energies and the second-order pair energies, which represent (for the M and LM shells) very close approximations to the ‘‘all external’’ pair correlation energies. It is found that the PW increments change in a highly regular way according to the rules previously found for the K- and L-shell electrons of the Ne-isoelectronic sequence. All pair energies calculated in this work disclose a monotone Z dependence, which is not the case for the Ne-like systems. Some attention is paid to the impact of the 4s2 electrons on the correlation energies for the M shell, which turned out to be very small.
Electronic structure of some heteronuclear diatomic molecules in the local spin density approximation
Authors: Dhar S. , Ziegler A. , Kanhere D. G. , Callaway J.
Published: July 2002

Ab initio self-consistent spin polarized calculations have been performed for the electronic structure of the heteronuclear diatomic molecules LiH, CO, and NO; using local spin density functional theory. The Kohn–Sham functions have been expanded in terms of a basis set of Gaussian orbitals. All the one and two electron integrals are calculated exactly. The matrix elements of the exchange correlation potential are computed numerically using a two dimensional doubling grid developed for this purpose. The total energy, the binding energy, the equilibrium distance, the vibrational frequency, and the dipole moment are reported and compared with experimental results and with other calculations. The agreement of our results with experimental values is very good in all cases.
Infrared spectra (2–16 μm) of ArI Rydberg emission from a microwave discharge plasma
Authors: Rawlins W. T. , Gelb A. , Armstrong R. A.
Published: July 2002

Infrared (2–16 μm) emission from Ar Rydberg atoms, excited in a conventional low-pressure microwave discharge plasma, has been observed in the cryogenic COCHISE reactor/spectrometer facility. The observed spectrum is very complex but is identifiable using the detailed energy level structure and optical selection rules for ArI. Detailed transition probabilities for dipole-allowed transitions between 2 and 16 μm were computed using the Coulomb approximation. Comparisons of observed and predicted spectra show that substantial long wavelength infrared (LWIR) emission (∼12 μm) arises from Rydberg states near the ionization limit; these states must have kinetically enhanced populations in order to account for the observed emission intensities. The results are interpreted in terms of a radiative/collisional cascade sequence initiated by dissociative recombination of Ar+2 with energetic electrons in the active discharge.
Dynamics of selected rovibronic B 3Π(0+) states of IF: Variation of the electronic transition moment with internuclear distance
Authors: Trautmann M. , Wanner J. , Zhou S. K. , Vidal C. R.
Published: July 2002

Rovibronic levels of the IF B 3Π(0+) state have been selectively excited using a cw dye laser in a crossed-molecular-beam experiment in which IF molecules were synthesized in the X 1∑+ ground state. Einstein A coefficients have been obtained from the fluorescence spectra. RKR potentials, Franck–Condon factors, and r centroids have been calculated using recently determined molecular constants for the X and the B state. The r-centroid approximation was found to be valid for the B–X system of IF and the variation of the electronic transition moment with the internuclear distance was determined. Over a range of the internuclear distance, 1.9<r<2.4 Å, the electronic transition moment was found to increase by as much as a factor of 2.4.
Determination of the number of effective charges of colloidal particles by transference measurements
Authors: Ito Kensaku , Ise Norio , Okubo Tsuneo
Published: July 2002

The number of effective charges of colloidal particles was determined for polystyrene-based polymer latices by transference measurement. The fraction of free counterions (f) was surprisingly low and appeared to decrease with the analytical valency; the f values were about 0.1 for a latex having 1.7×104 SO3H groups per particle. A more highly charged latex (with 7.2×105 sulfonate groups) had f values of about 0.04. These values are definitely smaller than those reported for soluble polyelectrolytes (about 0.4).
The Prüfer phase function calculation of complex energy eigenvalues for cubic anharmonic oscillator
Authors: Pajunen Petri , Luppi Jussi
Published: July 2002

The Prüfer phase function method is applied to calculation of complex energy eigenvalues of a cubic anharmonic oscillator model potential. The method yields accurate resonance energies and widths and an unambiguous prescription for the quantization path on which the solution has the usual oscillatory property familiar with the bound state wave functions.
Electron photodetachment from transient negative ions in the multiphoton ionization of CH3I
Authors: Chupka William A. , Woodard Anne M. , Colson Steven D. , White Michael G.
Published: July 2002

Photoelectron spectra produced by the laser multiphoton ionization of CH3I show a strong band due to absorption of an additional photon above the ionization threshold and resembling either inverse bremsstrahlung or ‘‘above threshold ionization.’’ The spectra are ascribed to a process of capture of Coulomb-retarded photoelectrons to form transient CH3I− ions which are then photodetached before, during and after dissociation to CH3+I− products. Both CH−3 and I− ions are observed. Several aspects of the process are discussed in terms of a potential energy diagram.
Isotope effects on the populations of metastable H3 and D3 molecules in neutralized ion beams
Authors: Jeon Seung-Joon , Raksit Asit B. , Gellene Gregory I. , Porter Richard F.
Published: July 2002

The relative abundances of metastable H*3 and D*3 molecules in collimated beams of neutralized ions are analyzed by the technique of collisional reionization (charge stripping). The fraction of metastable/dissociative species formed in the electron transfer process H+3(D+3)+K(g) → H*3(D*3)+K+ diminishes if the precursor ions have excess internal energy. The abundance ratio of H*3/D*3 for equivalent 6 keV beam fluxes increases sharply when the time span between neutralization and reionization is increased. The measurements show that a state of D*3 with low rotational quantum numbers (N>0) is decaying on the time scale of the beam transit with a lifetime of about 0.2 μs. Results are interpreted in reference to the predissociation behavior of the 2p 2A2 electronic state of the radical. The disproportionate ratio of IH*3/ID*3 ≫ 1 is a consequence of the relative abundances of precursor levels in H+3 and D+3 that can transform into metastables by electron transfer.
Spectroscopy of rare gas hydrogen halide complexes
Authors: Bernstein Lawrence S. , Wormhoudt Joda
Published: July 2002

A recently developed band contour model is used to analyze the gas phase spectra of rare gas hydrogen halide complexes in the region of the hydrogen halide fundamental. The sensitivity of model predicted spectra to variation of major spectroscopic parameters is illustrated for ArHCl. Published spectra from several groups for KrHCl, XeHCl, ArHBr, and XeHBr are considered. The unusual appearance of the XeHCl spectrum is attributed to the large shift of the HCl fundamental frequency −12.5 cm−1 when complexed to Xe. Through spectral analysis the dissociation energies of these complexes were found to be 214 (KrHCl), 220 (XeHCl), 220 (ArHBr), and 300 cm−1 (XeHBr). The uncertainty in these dissociation energies and comparison to other estimates are discussed.
Brownian dynamics simulation of stiff dumbbells
Authors: Hammouda Boualem
Published: July 2002

The effects of stiffness on the diffusion-limited dynamics of dumbbells in solution is studied numerically. The Langevin equation is used with two different models, the so-called Fraenkel and FENE dumbbells. It is found that the dynamics of rotation and stretching are dictated by the two following trends: (i) the density–density correlation function for these modes decays more slowly for larger values of the equilibrium distance between the two beads L (with the spring force constant K fixed), and (ii) it decays more quickly for increasing stiffness (with L fixed) making the bond stretching relaxation time τ2 smaller. For sufficiently stiff chains the value of τ2 becomes less than the delay time of the experimental correlator, resulting in a difference between the true and measurable first cumulants.
The microwave spectrum of the H2D+ ion: The 22 ← 221 transition
Authors: Saito Shuji , Kawaguchi Kentarou , Hirota Eizi
Published: July 2002

The 220 ← 221 transition of H2D+ was detected by using a dc discharge in a mixture of H2 and D2 with a hollow cathode cooled to liquid nitrogen temperature. The assignment was made on the basis of chemistry for production, the observed linewidth, and the lowering of the spectral intensity by the external magnetic field. The transition frequency was determined to be 155 987.185±0.037 MHz.
ESR study of the guanine cation
Authors: Close David M. , Sagstuen Einar , Nelson William H.
Published: July 2002

It has been proposed that the primary direct radiation damage products in DNA are guanine cations and thymine anions. Experiments reported here characterize a guanine cation observed in a single crystal of guanine:HCl:H2O. ESR experiments were performed by x-irradiating and observing the crystals at 15 K. Spectral parameters for the cation include N3 and N10 hyperfine couplings, a C8–Hα hyperfine coupling, and two small exchangeable couplings presumably from the N10 protons. The computed spin densities of ρ(N3)=0.283, ρ(N10)=0.168, and ρ(C8)=0.182 agree nicely with those observed for the guanine cation in DNA. In the single crystal the native molecule is protonated at N7. It is proposed that once the native molecule is oxidized it rapidly deprotonates at N7 to form the cation observed.
An exact result for the incoherent scattering function in dilute suspensions
Authors: Van Den Broeck C.
Published: July 2002

The effect of a square well potential added to the hard core repulsion, between particles in a dilute suspension, on their self-diffusion coefficient is investigated on the basis of the results, obtained by Batchelor, for the mobility of these particles. Hydrodynamic interactions are neglected. It is found that a moderately strong attractive potential leads to an increase of the self-diffusion coefficient, whereas a repulsive potential has the opposite effect. The exact result for the incoherent scattering function is given. The results for the self-diffusion coefficient are recovered in the long time limit. The short time behavior is also discussed and some conclusions are drawn.
Inhomogeneous broadening of electronic transitions of chromophores in crystals and glasses: Analysis of hole burning and fluorescence line narrowing experiments
Authors: Lee H. W. H. , Walsh C. A. , Fayer M. D.
Published: July 2002

A variety of nonphotochemical hole burning experiments are performed on the system pentacene (PC) in benzoic acid (BZA) crystals. These experiments and previously reported fluorescence line narrowing experiments are used to probe the nature of the inhomogeneous broadening of electronic transitions of chromophores in crystals and glasses. A microscopic model is presented which explains detailed results from both types of experiments. Two fundamental assumptions are made in formulating the model. First, there is a large degree of accidental degeneracy in the absolute energy distributions of the chromophores; i.e., molecules in different environments can have the same absolute energy. Second, this degeneracy is lifted when the electronic state is changed. Narrow band excitation of PC causes a well-defined change in the PC’s local environment, producing a narrow spectral hole in the inhomogeneously broadened PC absorption origin and an antihole which is spectrally well-separated from the PC origin. The microscopic model is successful in explaining experimental results on correlations between hole widths and antihole widths, hole positions and antihole positions, and in explaining fluorescence line narrowing experiments on the correlation between the frequencies of resonant and nonresonant fluorescence and the broadening of nonresonant fluorescence. The result is a microscopic picture which demonstrates that narrow band excitation of an inhomogeneously broadened electronic transition involves molecules with a very wide distribution of absolute energies.
Intramolecular electrical and dynamical interactions in formaldehyde: A discussion based on infrared intensity data
Authors: Castiglioni C. , Gussoni M. , Zerbi Giuseppe
Published: July 2002

In this paper the infrared intensities of formaldehyde d0 and d2 are interpreted on the basis of electro-optical parameters. It is shown that infrared intensities can be used as a powerful tool to electro-optical parameters. It is shown that infrared intensities can be used as a powerful tool to choose among different, even if reasonable, force fields: 16 force fields taken from literature have been examined and only a few of them have been found appropriate to fit infrared intensities. Both electrical and potential intramolecular interactions in CH2O support the hypothesis of a backdonation of electronic charge from the oxygen lone pairs to the CH bonds. An attempt to remove the amibguity in angular electro-optical parameters has been made on the basis of the ‘‘orbital following approximation.’’
A conjecture concerning transformation of a supercooled hard sphere liquid to a metastable disordered solid
Authors: Rice Stuart A. , Cerjan Charles , Bagchi Biman
Published: July 2002

It is conjectured that the hard sphere system has several distinct solid phases, all but one of which are metastable. The bifurcation theory analysis of freezing is extended to the description of the transition between a supercooled liquid and a disordered solid by defining a restricted phase space for the disordered solid. This approach leads to the prediction of a first order transition between a supercooled hard sphere fluid and a disordered metastable hard sphere solid. The results of the calculation are in qualitative agreement with the results of Woodcock’s molecular dynamics computer simulations.
Variational transition states for ion–molecule reactions
Authors: Truhlar Donald G.
Published: July 2002

Dodd discussion of  entropy bottlenecks  in their recently published paper is commented upon. It is pointed out that their argument is inconsistent with the variational bounding property of classical generalized transistor state theory. (AIP)
Can the Bloch equations describe the vibrational spectra of a reacting molecule?
Authors: MacPhail Richard A. , Strauss Herbert L.
Published: July 2002

The vibrational spectra of molecules that are rapidly interconverted among distinct species by very fast motions, for example, during ordinary chemical reactions or during the rotation of a molecule between different sites in a solid, are considered. The question of the title is addressed in a number of distinct stages. First, the spectra predicted by Bloch equations with the inclusion of exchange terms are derived. The results differ from those familiar from magnetic resonance spectroscopy, since the vibrational transition moment can have a different magnitude and orientation in each site. Next, the question of whether a reaction can be fast enough on the time scale required for the simple vibrational Bloch equations to be valid is addressed, and it is concluded that this is unlikely. The observed spectrum may be fit with the result of the Bloch equation analysis (as has been done often in the past), but we conclude that the rate of the reaction cannot be simply extracted from the parameters used in this analysis. Instead, a more useful and general analysis of the spectra proceeds from a correlation function approach. We briefly discuss the results of a Redfield analysis. Next, we use the Mori–Zwanzig formalism to derive equations for vibrational spectra of reacting molecules. We outline the assumptions that are necessary to simplify the Mori equations sufficiently to reproduce the Bloch equations. The most important assumption is that the reaction goes over a high barrier. However, this results in a reaction too slow to have an observable effect. For lower barriers, the effect of the motion along the reaction coordinate cannot be separated into a reactive and a nonreactive part. This analysis demonstrates, in detail, the failure of the simple Bloch equations with exchange. Observed spectra can be interpreted using the equations derived from a Redfield or a Mori analysis.
Calculation of the self-diffusion coefficient of interacting Brownian particles based on the time-independent Smoluchowski equation
Authors: Yoshida Nobuo
Published: July 2002

A method of calculating the first-order concentration dependence of the self-diffusion coefficient of spherical Brownian particles interacting with one another is derived on the basis of the time-independent (i.e., stationary) form of the two-particle Smoluchowski equation. The method is applied to the cases of hard spheres with and without hydrodynamic interactions. The hydrodynamic interactions are taken into account by use of Oseen’s and Felderhof ’s approximations for the diffusion tensors. Explicit expressions for the self-diffusion coefficient are obtained which are in agreement with previous ones based on the time-dependent (i.e., nonstationary) form of the Smoluchowski equation.
Diagrammatic representation in the recursive residue generation method: Multiphoton excitation of an active mode coupled to a molecular background
Authors: Schek Israel , Wyatt Robert E.
Published: July 2002

A diagrammatic representation for the chain elements in the tridiagonal representation of a Hamiltonian is developed for the mutliphoton excitation of a molecular active mode which is coupled to a background of radiatively inactive modes. Both harmonic and anharmonic models for the active mode are discussed. Statistical level congestion of the background modes is discussed and we show the relative importance of various diagrammatic paths for both strong and weak laser intensities.
The solution of the Schrödinger equation in imaginary time by Green’s function Monte Carlo. The rigorous sampling of the attractive Coulomb singularity
Authors: Skinner Douglas W. , Moskowitz Jules W. , Lee Michael A. , Whitlock Paula A. , Schmidt K. E.
Published: July 2002

We present a new Green’s function Monte Carlo method for solving for the ground state of the Schrödinger equation. Unlike the commonly used short time approximation this method has no time step error. We formulate the method so that the attractive Coulomb singularities are isolated and can be accurately sampled. The algorithm is used to obtain the ground state energies of the following atomic systems: H, He and the helium-like ions of Be, N, and O. The results compare favorably with the experimental ground state energies.
Libron–phonon coupling effect on the infrared absorption spectra of molecules trapped in matrices
Authors: Garzón I. L. , Blaisten-Barojas Estela
Published: July 2002

The libron–phonon coupling (LPC) model is used to calculate the IR absorption coefficient of diatomic molecules trapped in solid matrices at low temperatures. The coupling between the collective motions of the crystal and the molecule libration-type motion is at the basis of the LPC model. This coupling results in temperature dependent shifts and broadening of the spectral lines even in the low temperature regime. The near IR experimental spectra of CO in Ne, Ar, Kr, and Xe matrices are successfully interpreted with the present theory. The strength of the libron–phonon coupling and other constants pertaining to the theory are reported. The far IR spectra is predicted as well.
Semiclassical reaction-path methods applied to calculate the tunneling splitting in ammonia
Authors: Brown Franklin B. , Tucker Susan C. , Truhlar Donald G.
Published: July 2002

The small-curvature semiclassical adiabatic (SCSA) approximation, which is based on a reaction-path Hamiltonian, is used to calculate the rate of interconversion of the ammonia invertomers. In these calculations, we employ two realistic potential energy surfaces for which accurate tunneling splittings have been calculated previously. The semiclassical method is shown to be accurate within 16% for this prototype quantal isomerization rate.
Energy transfer in condensed media. II. Comparison of stochastic Liouville equations
Authors: Brown David W. , Lindenberg Katja , West Bruce J.
Published: July 2002

The linearized form of the transport theory recently developed by West and Lindenberg is used to obtain an approximate equation of motion for the density matrix of an exciton confined to a dimer. The resulting equation has a form which may be readily compared with others derived from both dynamical and phenomenological approaches. Comparisons are made between the equations of motion, optical spectra, and generalized master equation memory functions which result from the theories considered.
A theoretical investigation of the UV spectrum of ethyl radical
Authors: Blomberg M. R. A. , Liu B.
Published: July 2002

A b initio multiconfiguration self-consistent field and configuration interaction calculations show that the ethyl radical when vertically excited from its ground state to the lowest 3p Rydberg state dissociates without a barrier to ground state methyl radical and 1B1 methylene, which accounts for the continuous nature of the ethyl spectrum. It is also shown that the 3p Rydberg states of ethyl are lower in energy in the nonclassical (hydrogen bridged) equilibrium structure of the ethyl cation than in the classical ground state ethyl radical equilibrium structure or at their respective adiabatic dissociation limits. This suggests the equilibrium structures of the 3p Rydberg states are nonclassical.
Bonding in metal hexacarbonyls
Authors: Arratia-Perez Ramiro , Yang Cary Y.
Published: July 2002

A detailed analysis of the valence molecular orbitals (MO) in Cr(CO)6, Mo(CO)6, and W(CO)6 is presented. A generalized bonding scheme, which includes participation of metal p electrons in the metal–ligand bond, emerges from our results. The metal p electrons are also responsible for effecting mixings between different sets of carbonyl 5σ and 1π orbitals. In these hexacarbonyls, this ‘‘σ’’+‘‘π’’ metal–ligand bonding contribution is quantitatively as significant as the well known σ donation and π-back-donation components. The MO’s obtained with the Dirac scattered-wave (DSW) method are also used to determine the importance of relativistic effects in this series. The DSW results show that even in W(CO)6, relativistic effects are qualitatively unimportant. Extensive comparisons with existing theoretical and experimental data are made for both ground-state and transition-state calculations.
Proton spin relaxations in solutions of paramagnetic complex with S=3/2 in slow motion region
Authors: Hwang Lian-Pin , Ju Chang-Yuan
Published: July 2002

Proton NMR relaxation in paramagnetic systems of S=3/2 with electron spin relaxation in slow-motional region is examined. The proton relaxations arising from the modulations of scalar, dipolar, and scalar–dipolar cross interactions from paramagnetic spin by slow molecular motion together with their field dependence, the variation of zero field splitting (zfs) interaction, and internal rotation interference are investigated. The overall reorientational motion of the complex presumably gives rise to the fluctuation of zfs interaction. The model for independent modulations of dipolar and zfs interactions is considered also. The proton relaxation rates are directly calculated from the approach of solving stochastic Liouville equation for slow-motional ESR relaxations. Slow-motional effects on individual proton relaxation rates are discussed. The final results are appropriately modified to incorporate the influence of internal rotation for proton. The field-dependent methyl proton relaxation rates in tris-acetylacetonatochromium (III) complex are calculated. Effects due to various potential barriers in the internal rotation are also presented.
Semiclassical theory of resonances in 3D reactions. II. Resonant quasiperiodic orbits for F+H2
Authors: Marston C. Clay , Wyatt Robert E.
Published: July 2002

Numerical methods for the computation and semiclassical quantization of resonant orbits (to accurately predict resonance energies of the 3D, J=0, F+H2 reaction) are extended from the periodic trajectories of part I to the more general quasiperiodic trajectories. In addition, semiclassical quantization conditions are revised for application to newly discovered collinear resonant periodic orbits and comparative stability analysis is used to evaluate the relative significance of these alternative orbits for both the collinear and 3D reactions. The method used in this series for computing the bound classical trajectories is then compared with the more general RP method.
A critique of the Brownian approximation to the generalized Langevin equation in lattice dynamics
Authors: Diestler D. J. , Riley M. E.
Published: July 2002

We consider the classical motion of a harmonic lattice in which only those atoms in a certain subset of the lattice (primary zone) may interact with an external force. The formally exact generalized Langevin equation (GLE) for the primary zone is an appropriate description of the dynamics. We examine a previously proposed Brownian, or frictional damping, approximation that reduces the GLE to a set of coupled ordinary Langevin equations for the primary atoms. It is shown that the solution of these equations can contain undamped motion if there is more than one atom in the primary zone. Such motion is explicitly demonstrated for a model that has been used to describe energy transfer in atom–surface collisions. The inability of the standard Brownian approximation to yield an acceptable, physically meaningful result for primary zones comprising more than one atom suggests that the Brownian approximation may introduce other spurious dynamical effects. Further work on damping of correlated motion in lattices is needed.
On the measurement of molecular anisotropies using laser techniques. I. Polarized laser fluorescence
Authors: Bain A. J. , McCaffery A. J.
Published: July 2002

The tensor density matrix formalism is used to derive expressions for the circular and linear polarization of laser-induced fluorescence from molecules which have an anisotropic distribution in the spatial orientation of their ground state angular momentum components. The generalized anisotropic distribution is expressed as a series of state multipolar moments and it is shown that the excited state multipolar moments created therefrom by the absorption of laser radiation may be quite complex even in the absence of perturbations which cause cross relaxation. Under these circumstances, polarized laser fluorescence does not give an unambiguous measure of the ground state multipolar moments and in succeeding papers we discuss methods which do yield these quantities without ambiguity.
High resolution Raman spectra of the Fermi diad in crystalline CO2 at 6 K
Authors: Ouillon R. , Ranson P. , Califano S.
Published: July 2002

High resolution Raman spectra of the Fermi diad ω1:2ω2 in crystalline CO2 at 6 K were obtained by means of a tandem interferometer-spectrometer instrument. For the first time the two components of the factor group splitting of the Ω− hybrid level were perfectly resolved. The bandshape of the two overlapping components of the Ω+ state were obtained by means of polarization measurements. The very different residual bandwidths of these crystal modes are discussed in terms of decay processes involving the two-phonon continuum and the isotopic impurity levels.
Vibrational energy relaxation of hydrogen chloride in liquid and solid xenon solutions
Authors: Chesnoy J.
Published: July 2002

The vibrational energy relaxation has been studied for hydrogen chloride diluted in liquid and solid xenon near the fusion point. The v=1 relaxation time is measured in the liquid and in the solid vs concentration. On solidification of the xenon, we observe the continuity of the relaxation times for HCl isolated in the solution. This behavior, different from that observed for vibrational spectroscopy, points out the minor role played, for the relaxation behavior, by the symmetry of the site occupied by the hydrogen chloride molecule. In the solid phase, we measured the relaxation times for the first three excited vibrational states vs temperature up to the fusion point. After considering the importance of anharmonic coupling in the vibrational interaction for this system, we can understand our results in terms of binary approaches to vibrational relaxation currently applied to the liquid phase, thus underlying the unity of the relaxation process in the gas, liquid, and solid phases.
The temperature dependence of diffracted beam intensities in atom–surface scattering
Authors: Jackson Bret , Metiu Horia
Published: July 2002

We develop a new method for the calculation of the atom scattering analog of the Debye–Waller factor. Unlike x-ray and neutron scattering the properties of an atom scattered by a solid surface cannot be computed by perturbation theory; therefore the simple Debye–Waller theory cannot be applied. Nevertheless the Debye–Waller phenomenon has a close analog: the elastic intensity is depressed due to the uncorrelated part of the thermal motion of the lattice atoms. To compute this effect we develop a time dependent scattering theory in which the quantum properties of the scattered atom are described by propagating coherently an ensemble of wave packets and lattice motion is simulated by a classical Langevin equation. Applications are made to He and Ne scattering from a surface whose lattice dynamics mimics that of Pt(111) but whose corrugation was slightly increased to enrich the diffraction structure.
Variational calculations of rotational–vibrational energy levels of water
Authors: Chen Cheng-Lung , Maessen Bärbel , Wolfsberg Max
Published: July 2002

Calculations are carried out of the rotational–vibrational energy levels of H2O and D2O for J≤10 by a variational method. The full Watson Hamiltonian is employed, with the potential function in valence displacement coordinates and with the integrations over normal coordinates carried out by Gauss–Hermite quadrature. The basis set consists of products of vibrational functions and symmetric top functions; the vibrational functions diagonalize the Hamiltonian for J=0. Comparison is made with experiment, and also results obtained with different force fields are compared. The mixing of different vibrational functions into a wave function for a given rotational–vibrational state is studied; mixing is found to be quite prevalent.
Infrared spectra and band strengths of the fundamental and first overtone of HCl and DCl in liquid xenon solutions
Authors: Knudtson J. Thomas , Weitz Eric
Published: July 2002

The band strengths of the fundamental and first overtone of HCl and DCl have been measured in liquid xenon solution. The fundamental increases in intensity while the overtone decreases in intensity relative to the respective gas phase values. A variety of simple models are applied to the system in an effort to explain the observed effects. The possible effect of HCl–Xe complexes on the spectra is considered.
Electronic states of matrix-isolated Ni atoms: A magnetic circular and linear dichroism study
Authors: Vala Martin , Eyring Marc , Pyka Jan , Rivoal Jean-Claude , Grisolia Christian
Published: July 2002

The absorption, magnetic circular dichroism (MCD), and magnetic linear dichoism (MLD) spectra of Ni atoms isolated in an argon matrix (4.2 K) have been measured. By utilizing the complementarity of the predicted MCD and MLD signals for transitions to states of different J values, together with the known gas phase positions and relative intensities, an assignment for all observed bands has been made. Most bands in the region 360–270 nm originate from atoms in sites whose ground state is 3D3, whereas bands in the ∼240–230 nm region arise from atoms whose matrix ground state is 3F4. Thermal annealing results in the disappearance of the 3F4 ground state atoms, but not the 3D3 ground state ones.
Thermodynamics using effective spherical potentials for CO2 anisotropies
Authors: Johnson J. D. , Shaw M. S.
Published: July 2002

We examine the fluid thermodynamics of a model homonuclear diatomic system with anisotropies characteristic of CO2. The density (CO2 densities) and temperature regime is 1.6 g/cm3≲ρ≲2.6 g/cm3 and 1000 K≲T≲7000 K. Extensive molecular dynamics data for the model equation of state are presented. Comparisons are then made to the thermodynamics from three effective spherical potentials; the potential median, the radial median, and an exponential-six with parameters adjusted to best fit the true thermodynamics. The two median potentials typically give 3% agreement for the higher temperature fluid with a 5%–10% comparison nearer the freezing line for both pressure and internal energy while the fit is good to 3% or better. Thus there exists an effective spherical potential that very accurately models the thermodynamics of dense fluid CO2, a system whose potential energy in the repulsive region varies by three to four orders of magnitude as a function of angles with fixed center of mass separation. The median averages give an excellent representation of this effective spherical potential.
Theory of nonadiabatic gas–surface reactions
Authors: Olson J. A. , Garrison B. J.
Published: July 2002

A theoretical description of near-resonant charge-exchange processes occurring in gas–surface collisions is presented. The diatomics in molecules method is used for the electronic description of a surface consisting of five atoms. The gas–surface interaction potentials and couplings are obtained with the polyatomics in molecules approach. Trajectories for the ‘‘nuclear’’ variables and transition probabilities are calculated with the common eikonal formalism. Preliminary results are presented for Na scattering from a W(110) surface. The initial kinetic energy of the sodium atom is varied between 5 and 60 eV and its trajectory is restricted to be perpendicular to the surface and striking the center W atom. The results show a noticeable probability (≤20%) for electron transfer to the surface.
Observation of Λ doublet population inversion in the reaction C(1D2)+H2→CH(X 2π)+H
Authors: Jursich Gregory M. , Wiesenfeld John R.
Published: July 2002

Reaction of C(1D2) formed in the 157 nm laser photolysis of C3O2 with H2 results in the production of the CH radical. Laser induced fluorescence measurements made in both the unsaturated and saturated regimes reveal that this reaction has a propensity for formation of the higher-lying, π+, Λ doublet component. The preferential formation of the π+ component can be explained in terms of a mechanism in which dissociation of the CH2 (1A1) intermediate complex occurs with retention of the orientation of the half-filled p orbital in the plane of rotation of the departing CH fragment.
Intramolecular vibrational energy redistribution in CHCl3: A theoretical analysis
Authors: Kato Shigeki
Published: July 2002

The mechanism of intramolecular vibrational energy redistribution (IVR) in the vibrationally excited chloroform (CHCl3) has been studied theoretically. An analytic form of potential energy function was constructed with the aid of quadratic and cubic force constants calculated by ab initio MO method. Classical trajectory methods were applied to simulate the IVR process from the high CH stretch overtone states and the results were analyzed in terms of the moments of energy in each vibrational mode. The overtone absorption line shapes were also calculated. The results obtained are summarized as follows: (1) The IVR process is characterized by the two different time scales. The energy transfer from the CH stretch to the CH bend occurs rapidly, while it takes a longer time to complete the energy flow into the low frequency CCl vibrations. (2) There is a discontinuous transition of the mechanism of IVR between v=3 and 5. Above v=5, the energy in the CCl vibrations increases monotonically and the distribution in each mode can be represented by a simple exponential form, while the amount of energy transferred into the CCl modes is negligibly small for v=1–3.
Relaxation behavior in a bistable chemical system near the unstable steady state and separatrix
Authors: Pifer Tammy , Ganapathisubramanian N. , Showalter Kenneth
Published: July 2002

An investigation of relaxation behavior in the bistable iodate–arsenous acid reaction is presented. Relaxations from the unstable steady state and separatrix to a stable steady state are compared to model predictions. Relaxations from the unstable steady state are analyzed with a linearized model and relaxations from near the separatrix are explained in terms of a computed phase portrait.
Extinction coefficient of H2CC(3B2) at 137 nm
Authors: Fahr Askar , Laufer Allan H.
Published: July 2002

The extinction coefficient of H2CC(3B2) was obtained at 137 nm. The vinylidene radicals were produced from the flash photolysis of C2H3Cl and their concentration derived from the quantity of HCl produced in the photolysis. The measured extinction coefficient is 694±218 atm−1 cm−1.
Infrared multiphoton excitation of polyatomic molecules
Authors: Simpson T. B. , Black J. G. , Burak I. , Yablonovitch E. , Bloembergen N.
Published: July 2002

We present a systematic study of the infrared multiphoton excitation and dissociation of several polyatomic molecules. The molecules range in size from SO2, with three vibrational modes, to C3F7I, with 27. A gradual transition occurs from intensity dependent excitation, characteristic of a sparse density of vibrational states in small molecules, to a fluence dominated absorption characteristic of a quasicontinuum of vibrational states in large, heavy molecules. Molecules with ten or more atoms showed no intensity dependence under pulsed CO2 laser excitation at a fixed energy fluence. For a molecule to have a high probability of dissociation under realizable conditions of laser intensity and fluence, quasicontinuum region excitation must dominate. All molecules appeared to have statistically coupled vibrational modes at high levels of vibrational energy.
Reply to ‘‘Comment on ‘Effect of temperature on nondissociative electron attachment to perfluorobenzene’ ’’
Authors: Christophorou L. G.
Published: July 2002

The results of previously reported experiments on the electron attacment rate constant for perfluorobenzene are further discussed in the light of new results reported by Adams et al. and the previously publised results of Hernandez-Gil et al.3. (AIP)
V–V energy transfer from highly vibrationally excited azulene to CO2
Authors: Jalenak Wayne , Weston Ralph E. , Sears Trevor J. , Flynn George W.
Published: July 2002

The vibrational energy transfer in the azulene/CO2 system is studied. The vibrational excitation of CO2 and the relative populations of the CO2 ν2 and ν3 vibrational modes are studied experimentally by measuring the infrared emission intensities. (AIP)
Crystal structure of pyridazine and azabenzene crystals: A test for an intermolecular potential
Authors: Gamba Z.
Published: July 2002

An intermolecular potential for benzene and azabenzene crystals was tested by using it to reproduce the crystal structures of benzene, pyrimidine, pyrazine, the two known forms of s-triazine and tetrazine by molecular packing analysis. A Pmn21 (C72v) structure for the unknown crystal pyridazine is proposed.
Spin-orbit and spin-polarization effects in neptunium hexafluoride
Authors: Case David A.
Published: July 2002

Relativistic molecular orbital calculations in the multiple scattering approximation are reported for NpF6, and the results are used to calculate the molecular g tensor and hyperfine parameters for the Np and F nuclei. Core spin-polarization effects are estimated from quasirelativistic spin-unrestricted calculations, which are corrected in an approximate fashion for the effects of spin-orbit mixing. The calculated results (with experimental values in parentheses) are: g=−0.700 (−0.604); A(237Np)=−2.02 GHz (−2.00); a∥(19F)=−103 MHz (−132); and a⊥(19F)=−43 MHz (−42). These results are among the first nonempirical calculations of magnetic resonance parameters for actinide complexes. The calculations predict that the unpaired electron in NpF6 has 4% to 5% fluorine p character.
The inversion of diatomic spectra to estimates of population parameters
Authors: Prisant M. G. , Zare R. N.
Published: July 2002

A bivariate polynomial representation of rovibrational population distributions is developed. This representation permits direct reduction of diatomic fluorescence spectra from chemical dynamics experiments to estimates of rotational and vibrational parameters by means of a linear least squares procedure.
Intramolecular dynamics and multiresonant absorption spectroscopy. I. Reduced non-Franck–Condon intensity in the high-power two-photon absorption spectrum of NO2
Authors: Bigio Laurence , Grant Edward R.
Published: July 2002

The two-photon absorption spectrum of the X 2A1→3pσ 2∑+u transition in NO2 shows prominent Franck–Condon forbidden origins. The absolute intensities of these non-Franck–Condon transitions, as seen by ionization, diminishes at high power. A dense system of dissociative states lies intermediate at the level of the first photon. These states are highly mixed in either bent or linear zeroth-order basis, and thus at low power effectively bridge bent-to-linear origins. At high laser intensity, power (lifetime) broadening prepares a superposition state with the optical character of the ground state and thus poor overlap with low-lying linear excited states. The preparation and projection of this zeroth-order, nonstationary intermediate state bears strong analogy to similar absorption and fluorescence processes stimulated by picosecond pulses.
Ultraviolet photoemission spectra of organic single crystals
Authors: Sato Naoki , Inokuchi Hiroo , Schmid Bernhard M. , Karl Norbert
Published: July 2002

Photoelectron spectra of single crystals of eight aromatic compounds were measured at several UV wavelengths. Useful results were obtained when sample charging was eliminated by inducing photoconduction through subsidiary illumination of the sample crystal with low energy light, and/or by a vapor-deposited gold grid on the sample surface. The threshold ionization potential obtained for a single crystal was found always to be lower than that for the corresponding polycrystalline film.
A proposed neutron diffraction experiment to measure hydrogen isotope fractionation in solution
Authors: Newton Marshall D. , Friedman Harold L.
Published: July 2002

A novel method for investigating solute–solvent H/D exchange equilibria in aqueous solution is described. The ‘‘first-order difference’’ neutron diffraction method of Enderby and co-workers is combined with a variation of the isotopic composition of the solvent, ideally from pure D2O to that D2O–H2O mixture in which the average neutron scattering length of the H and D species vanishes. The new technique can give the location of the exchange site with respect to a particular atom as well as the H/D exchange constant for the site with reference to the bulk solvent. The relevant solution thermodynamic data are reviewed to identify systems for which the proposed neutron diffraction experiment is feasible. The literature data are complemented by new calculations of the effect of an ion on the O–H stretch vibration and the libration of the neighboring water. For +3 ions the dominant isotope effect is associated with the O–H stretch of the water; the shift to lower frequencies is proportional to the square of the ionic charge z in the sequence Na+, Mg2+, Al3+, while the libration frequency increases linearly with z in the same series. The reported free energy data for H2O to D2O transfers of various Mz+ ions can be understood on the basis of these observations. Finally, while the question of feasibility of the new technique invites examination of the details of ionic hydration, the main point is that such details could be elucidated by the proposed diffraction technique.
Nonadiabatic interactions of anharmonically coupled oscillators
Authors: Dang T. Tung Nguyen
Published: July 2002

The validity of the adiabatic approximation applied to systems of two coupled oscillators–typically represented by the Henon–Heiles’ Hamiltonian–is examined. Through explicit analytical estimates of nonadiabatic couplings, it is shown that the adiabatic approximation is appropriate in all cases, except for the case of 1:1 Fermi resonance between the two oscillators. In this case, nonadiabatic couplings are found to be important already at an excitation energy of about two quanta, i.e., at much lower energies than Ec, the critical energy for the classically observed quasiperiodic–chaotic transition. Nonadiabatic interactions are dominantly horizontal at these energies (E<Ec), however, indicating some regularity in the energy spectrum at low excitation, despite the early breakdown of the adiabatic separation.