bluuebunny/crossref_metadata_2025 huggingface dataset:
Lifetimes of degenerate benzene 1B2u levels split by vibrational angular momentum
Authors: Rosman Ron L. , Villaeys Albert A. , Freed Karl F. , Rice Stuart A.
Published: July 2002

This work examines, both experimentally and theoretically, the lifetimes of nominally degenerate benzene 1B2u levels split by differential coupling of the vibrational angular momentum components. We report fluorescence lifetimes for the 61162, 61102, and 61172 levels of the S1 electronic state in cold C6D6 in a supersonic jet. The higher energy vibrational angular momentum component has the longer lifetime. Calculations of the nonradiative decay rates for these levels are presented. Calculations based on conventional radiationless transition theory, assuming the prepared state is a single vibronic level, are not able to explain the experimental results, and we conclude that another mechanism must be responsible for the observed lifetime differences. We present a qualitative explanation of the data that takes into account perturbations of zeroth-order harmonic oscillator states by cubic and quartic vibrational anharmonicities and by Coriolis coupling. These perturbations affect the split vibrational angular momentum components differently and are capable of producing differences in lifetimes.
Optically detected stimulated spin echoes of phosphorescent F2+2 defects in calcium oxide
Authors: Vreeker R. , Glasbeek M.
Published: July 2002

Using techniques for the optical detection of stimulated spin echo transients, nonstationary spin diffusion is observed (at 1.2 K) for F2+2 centers, in CaO, in the photoexcited 3B1 state. The spin diffusion is caused by magnetic dipolar interactions between the S=1 spins of photoexcited F2+2 centers and flipping S=1/2 spins of F+ centers. From the experiments, the characteristic strength of the F2+2– F+ spin–spin interactions can be determined; this characteristic strength was found to be dependent on the laser wavelength used for the optical excitation of the F2+2 centers.
Determination of an experimental He2 potential energy function by inversion of differential cross sections
Authors: Lambrakos Sam G. , Peterson Norman C.
Published: July 2002

Recently reported differential cross sections for scattering of high-velocity neutral helium atoms from helium gas were analyzed using a Firsov inversion procedure. This procedure constrains the initial conditions of the inversion to be consistent with data independent of scattering measurements and limits the inversion to experimental conditions where elastic scattering predominates. The repulsive potential energy of a pair of ground state helium atoms is reported for internuclear separations of 0.5 to 1.0 Å.
Time-resolved stimulated Raman scattering in a diamond anvil cell
Authors: Baggen Michael , van Exter Martin , Lagendijk Ad
Published: July 2002

We demonstrate the first application of picosecond stimulated Raman scattering in a diamond anvil cell. A study of vibrational relaxation as a function of pressure is made. As a model system, we choose the totally symmetric C–C stretching mode of benzene and benzene-d6. Measurements of the transverse relaxation time have been performed at room temperature in the pressure range up to 5 GPa. A pronounced difference in the pressure dependence of the relaxation time is observed between the fluid phase, solid phase I, and solid phase II. We also observed another interesting phenomenon: the ratio of the isotropic Raman and nonresonant contribution to the nonlinear susceptibility appears to increase with pressure.
Comment on ‘‘A critique of the Brownian approximation to the generalized Langevin equation in lattice dynamics’’
Authors: Rodger P. Mark
Published: July 2002

The undamped modes found by Diestler and Riley [J. Chem. Phys. 83, 3584 (1985)] to arise in Brownian lattice dynamics are shown to be a real, though unobservable, consequence of the consideration of a zero frequency limit. As a result, it is shown that dissipative processes (such as those described by Brownian motion theory) need to be considered to arise as a ‘‘plateau’’ behavior of a system at long times (or small frequencies), and not as an infinite time (zero frequency) limit.
Vibrationally excited O2 in flames: Measurements on v″=9–11 by laser-induced fluorescence
Authors: Copeland Richard A. , Cosby Philip C. , Crosley David R. , Jeffries Jay B. , Slanger Tom G.
Published: July 2002

Vibrationally-excited ground state O2 is detected in a CH4/O2 flame in levels v″=9–11 by laser-induced fluorescence in the B 3Σ−u–X 3Σ−g Schumann–Runge system. Accurate line positions are measured by calibration against OH(A–X) lines appearing in the same spectra. Signal levels indicate that measurements up to at least v″=18 should be practical in such flames. The absolute energies of the three vibrational levels agree very well with RKR calculations of Albritton, based on earlier experimental work, but there is substantial disagreement for v″=11 with the extensive data of Creek and Nicholls.
Anharmonic forced Rayleigh scattering: A technique for study of saturated absorption in liquids
Authors: McGraw Daniel J. , Michaelson Jeffrey , Harris Joel M.
Published: July 2002

The technique of anharmonic forced Rayleigh scattering is developed and applied to the study of saturated absorption in liquids. Isobaric heating following saturated absorption at a crossed beam interference pattern creates an anharmonic transient thermal grating containing harmonics of the single spatial frequency present in the intensity. Diffraction observed for a probe beam incident at the Bragg angle for the second harmonic grating component provides a zero-background measurement of a deviation from linear absorption. Gaussian spatial and temporal beam profiles are taken into account and the angular sensitivity of the grating is measured and compared with theory. Transient decay rates are also measured and found to be in good agreement with the theory. A four-level saturation model is developed, and the saturation parameter Isat is related to kinetic parameters for the two dominant causes of saturation in liquids: intermediate state ‘‘bottlenecking’’ and photochemical change. The lack of second order diffraction from azulene in CCl4 allows us to put limits on the saturation intensity, photochemical yield, excited state cross section, and two-photon cross section of this molecule. The relative diffraction efficiency and dependence on excitation intensity of two diffraction orders are used to determine the nonrecombinant dissociation yields of I2 (excited at 532 nm) in hexadecane and hexane. The dissociation yields are 0.038 and 0.153, respectively.
A ground state steepest descent perturbation theory
Authors: Cioslowski J.
Published: July 2002

An entirely new approach to ground state perturbation theory is presented which is based on the application of the steepest descent technique to improve the estimate of the ground state energy. Unlike other perturbation theories this does not require either infinite summation over states or the solution of a differential equation. Moreover the computed energy is an upper bound to the true one. Several numerical examples are given exhibiting the improved performance of the new method over the traditional Rayleigh–Schrödinger perturbation theory (RSPT).
Origin of NMR temperature shift and electronic structure of vanadocene
Authors: Eicher H. , Köhler Frank H. , Cao Ren-de
Published: July 2002

The 13C and 1H NMR spectra of vanodocene were measured in the temperature range 208–377 K and compared with theory. To this end, the 3d3 term scheme of vanodocene is evaluated by a Hamiltonian which involves the Coulomb repulsion of the d electrons, their interaction with the D5d -coordinated ligands, and spin-orbit coupling. The adjustable parameters are chosen to fit the experimental ESR data and the weak bands at the low-energy side of the absorption spectrum. The reduced NMR shifts T(ΔH/H) of 13C and 1H, as calculated from the fine structure of the electronic ground state, depend on the well-known spatial structure, the ESR parameters, and on the adjustable radial spin densities at the ligand nuclei. In both cases only a slight temperature dependence is to be expected due to the orbitally nondegenerate ground state. This is in contradiction with the observed temperature slope of the reduced carbon shift. Thus, two modifications of the original assumptions are discussed. In the first place, the ligand-centered dipolar contribution is investigated theoretically. Although this effect improves the fit of both sets of spectra, it seems probable that in addition the nuclear coordinates change about 1% within the observed temperature range. The radial spin densities of vanadocene, however, are independent of the details of the fit procedure, yielding u2F(C) =−0.124(3) Å−3 and u2F(H) =+0.0982(2) Å−3 for the carbons and protons, respectively.
Size of a polyelectrolyte chain in solution containing counterions
Authors: Chen Y. , Kholodenko A. L.
Published: July 2002

Using the method of Edwards and Singh we calculate the mean square radius 〈R2〉 of the polyelectrolyte chain in solution containing counterions for the temperature greater than the Flory’s θ temperature. For the counterion density n we obtain: (a) 〈R2〉∝L2 when n→0, and (b) 〈R2〉∝L6/5 when n→∞. These results are in agreement with the Flory-type calculations and recent Monte Carlo simulations performed by Baumgärtner.
Experimental test of induced rigidity
Authors: Fincher Curtis R. , Gochanour Craig R.
Published: July 2002

Recent theoretical models for the nematic phase of semiflexible polymer chains predict a strong coupling between order and the conformational degrees of freedom of the chain. The presence of order in the nematic phase results in a strong preference for linear or rod-like conformations over flexible, random coil conformations. This conformational selection or induced rigidity is predicted to be general phenomenon associated with semiflexible chains. We have tested these predictions using a soluble polydiacetylene (4BCMU) as a probe. The 4BCMU chain undergoes a conformational transition (rod–coil) as a function of temperature in toluene which is accompanied by a large change in optical properties allowing the conformational transition to be followed spectroscopically in extremely dilute solutions. 4BCMU is miscible with both isotropic and nematic solutions of poly-(n-hexyl isocyanate) in toluene. If current models of induced rigidity are accurate, there should be a large shift in the transition temperature for the 4BCMU transition in nematic poly-(n-hexyl isocyanate) solutions. Experimentally we find no shift in the transition for nematic solutions when compared to dilute isotropic solutions. Possible explanations for the discrepancy between theory and experiment are discussed.
Induced dipole moment of physisorbed rare gas atoms
Authors: Van Labeke D. , Vigoureux J. M. , Grossel Ph.
Published: July 2002

We discuss models used for numerical estimations of induced dipoles in physisorption. In the case of perfect mirror the harmonic oscillator and Unsöld models are compared to the exact calculation done by using a coefficient introduced by Byers-Brown and Whisnant; which leads us to give, for the first time, an accurate value of the induced dipole for hydrogen and rare gas atoms. Even for more realistic surfaces the oscillator and the Unsöld models underestimate the dipole moment.
Inverse problems in chemical dynamics: The calculation of inverse coefficients
Authors: Guzman Robert , Rabitz Herschel
Published: July 2002

A general technique is described for gaining insight into inversion processes. Upon solving the equation of motion associated with a given physical model, specialized inverse coefficients are calculated to address questions on inverse modeling. The number of accessible independent inverse coefficients is shown to be directly related to the number of independent pieces of modeling data taken as available. Although the inverse coefficients do not in themselves form an inversion algorithm, they do give a quantitative measure of the importance of performing certain additional measurements for the ultimate purpose of inversion. The concepts are illustrated by some simple dynamical models. The calculations show that the normal forward sensitivities and the new inverse coefficients generally exhibit disparate behavior in accord with the differing physical quantities being addressed.
1H/29Si cross-polarization dynamics in amorphous hydrogenated silicon
Authors: Zumbulyadis N.
Published: July 2002

A modified cross-polarization method is used to simplify the solid-state magic-angle spinning 29Si-NMR spectrum of a-Si:H. At least three magnetically distinct environments are resolved. A microscopic model for the cross-polarization dynamics is used to assign the components of the spectrum. Contrary to expectations from solution state studies of low-molecular-weight silanes, the signals from 29Si bonded directly to hydrogen are shifted to a lower field compared to quaternary Si. This observation is rationalized on the basis of theoretical models and photoemission spectroscopy results published by other groups. A suggestion for the nature of shallow states is offered on the basis of the NMR results.
The vibrational force constant and transition stress for diatomic molecules
Authors: Zhang Yongfeng , Hanson David M.
Published: July 2002

The approximate orbital additivity of vibrational force constants for diatomic molecules is demonstrated. For a given molecule or molecular ion, vibrational force constants of excited electronic states associated with a particular configuration are approximately equal, provided configuration interaction can be neglected. The transition stress associated with an electronic transition strongly affects the vibrational motion. The vibrational force constant is shown to depend on the transition stress. The general relation between the force constant and the bond length for excited states is discussed. Molecular constants of excited states of diatomic molecules and molecular ions can be calculated from the transition stress. These calculated values are in good agreement with experimental results or with the theoretical values obtained by ab initio calculation.
Resonant multiphoton ionization spectrum and electronic structure of CH radical. New states and assignments above 50 000 cm−1
Authors: Chen Peter , Pallix Joan B. , Chupka William A. , Colson Steven D.
Published: July 2002

Resonant multiphoton ionization spectra, with mass and photoelectron analysis, of photolytically produced CH radical yields previously unobserved bands arising from two-photon transitions to Rydberg and highly excited valence states. Rotational analysis of the spectrum for m/e=13, coupled with vibrational labeling of the resonant state by photoelectron kinetic energy analysis, identifies a new state, designated E′ 2Σ+. Breaking off of rotational structure near N′=11 in the v=2 level of the D 2Πi state is attributed to predissociation by a doubly excited potential curve calculated to lie in this energy region. Comparison is made with earlier absorption spectra taken following flash photolysis.
Site-selective spectroscopy of hydrogenic sites in CaF2:Er3+ crystals
Authors: Cockroft N. J. , Thompson D. , Jones G. D. , Syme R. W. G.
Published: July 2002

Laser selective excitation and optical absorption studies of hydrogenated CaF2:0.05% Er3+ crystals have revealed 16 Er3+ ion sites involving H− or D− ion charge compensation. The relative occurrence of these sites can be controlled over a wide range by varying the duration of the hydrogenation treatment. The hydrogenic nature of these sites is established by the observation of local mode absorption lines in the infrared, Er3+ ion electronic line isotope shifts and associated local mode vibronic lines involving the H− and D− ions. Local mode infrared absorption frequencies of four sites are reported for most rare-earth ions. Five new Er3+−F− sites were identified in the laser selective excitation study. For 〈100〉 and 〈111〉 oriented crystals the fluorescence spectra of several of the sites exhibit well-defined polarization which determines their Er3+ ion site symmetries. Symmetry confirmations are also established for the two previously reported single Er3+ ion sites involving fluoride ion compensation. Eleven of the hydrogenic sites reported here are classified into two families, each derived from a single Er3+ ion site of the parent crystal, while three others are attributed to sites of nearly cubic Er3+ ion symmetry. Detailed spectroscopic results for these sites are presented, together with a crystal-field analysis for the C4v symmetry sites and some model assignments.
Correlated particles expansion applied to the hard sphere solid
Authors: Hardy Robert J. , Day Michael A.
Published: July 2002

The correlated particles expansion (CPE), which was described in detail in an earlier article, is used to calculate the configurational free energy, the compressibility factor, the Lindemann parameter, and the radial distribution function of a hard sphere solid. Two sets of results are presented: one set is accurate through second order in the CPE; the other is accurate through third order. The results for the free energy, the Lindemann parameter, etc. are in excellent agreement with the Monte Carlo (MC) values at small volumes and are in good agreement at the melting volume. However, slightly below the melting volume there is a kink in the free energy which causes a discontinuity in the compressibility factor. The kink results from a difficulty that arises in the solution of a set of self-consistent equations.
Collision-induced dissociation of laser-excited Br2[B 3Π(0+u);v′, J′]: Formation of Br*(2P1/2)+Br(2P3/2) at energies 1–5 k
T below dissociation
Authors: Smedley John E. , Haugen Harold K. , Leone Stephen R.
Published: July 2002

Absolute rate constants are measured for the dissociation of initially excited Br2[B 3Π(0+u);v′,J′] into Br*(2P1/2)+Br(2P3/2) fragments by thermal energy collisions with Br2(X 1Σ+g), Xe, and Ar at 297 K. A 0.04 cm−1 étalon-narrowed pulsed dye laser populates specific rovibrational levels of isotopic Br2 which are 1–5 kT below the B-state dissociation limit; in addition the laser directly photodissociates molecules which are in thermally excited vibrational levels. The method used to determine the absolute rate constants combines four sets of experimental determinations, which include infrared detection of Br*, visible Br2(B) fluorescence lifetimes, absorption spectroscopy of Br2 (B←X), and transient gain-vs-absorption spectroscopy on Br/Br*. At 1 kT below the dissociation limit, the absolute rate constants for collisional dissociation to Br*+Br are 2.9×10−10, 1.2×10−10, and 5.4×10−11 cm3 molecule−1 s−1 for Br2, Xe, and Ar, respectively. The results represent an average of some rotational and vibrational states grouped around a particular energy since rotational and vibrational energy transfer occur on a competitive time scale. The other major process that contributes to the total quenching rate is collision-induced predissociation to Br+Br. At 1 kT below the B-state dissociation limit, ∼75% of the quenching proceeds upward in energy to form Br*+Br, while at 5 kT this fraction is ∼8%. The efficiency of upward collisional dissociation correlates with the relative translational energy available.
Saturation and nonlinear electromagnetic field effects in the picosecond resonance Raman spectra of β-carotene
Authors: Carroll P. J. , Brus L. E.
Published: July 2002

The ground state resonance Raman spectra of β-carotene, in fluid isopentane at 293 and 119 K, show saturation and near-Lorentzian broadening as a function of fluence, using intense ∼30 ps visible laser pulses. There are no lines assignable to transient species. A two-pulse, two-color pump-and-probe Raman experiment shows that the broadening is due to high optical field, and not due to unrelaxed internal excitation in the molecule. The broadening is a manifestation of nonlinear resonance Raman scattering, previously predicted (but not observed) in molecules when the Rabi energy becomes larger than the vibrational dephasing linewidth. Our data can be semiquantitatively explained using a model by Dick and Hochstrasser. The saturation represents population loss from the vibrationally relaxed ground electronic state, and is consistent with lowest excited singlet lifetime on the order of 10 ps.
Iterative maps for broadband excitation of transverse coherence in two level systems
Authors: Cho H. , Pines A.
Published: July 2002

An iterative scheme has been used to derive a pulse sequence, compensated for off-resonance and rf inhomogeneity pulse errors, which implements a π/2 rotation of the spin density operator around a well-defined axis in the transverse plane. A fixed point analysis is applied to this and other iterative schemes revealing the source and nature of the compensation. Contrasting features of the different schemes are uniquely revealed by this analysis. General considerations for the construction of iterative schemes with other stable fixed sets are considered.
Quadrupolar binary fluid mixtures critical lines from a hard-sphere Lennard-Jones quadrupolar molecular model
Authors: Scalise O. H. , Zarragoicoechea G. J. , Rodríguez A. E. , Gianotti R. D.
Published: July 2002

The critical behavior of binary mixtures of fluids with permanent quadrupole moments is investigated by the application of the thermodynamic perturbation theory. Here the pair potential function is represented as a hard-sphere reference system being perturbed by the Lennard-Jones potential plus a quadrupole–quadrupole interaction. Good agreement with experimental critical loci is found for N2–H2, N2–He, CO2–C2H6, and CO2–C2H4 binary mixtures.
A 2D-exchange separated local field (EXSLF) experiment: An application to a 13C–1H isolated spin system in the solid state
Authors: Takegoshi K. , McDowell C. A.
Published: July 2002

To understand the spin dynamics involved in double resonance NMR experiments, rate constants for the flip–flop spin exchange process between a 1H spin coupled with a 13C spin and the surrounding 1H spins were determined in the absence of perturbing rf fields, and also under the influence of both 1H and 13C rf fields. To determine the flip–flop rate in the absence of the rf fields, we developed a new technique, the exchange separated local field (EXSLF) experiment. The EXSLF experiment was applied to the CH group in a single crystal of dimedone, for two different orientations of the crystal relative to the static magnetic field. The inverse of the flip–flop exchange rates determined by the EXSLF experiments are 276 and 391 μs for the orientations B0//b and B0//c*, respectively. The flip–flop exchange motion under the influence of both 1H and 13C rf fields was also studied by examining the transient oscillation phenomena occurring during a spin-locking cross-polarization experiment. The values obtained for the inverse of the rate constants for the flip–flop exchange motion were 450 and 540 μs for B0//b and B0//c*, respectively. The observed slow flip–flop rates show that the 1H–13C coupled spin system in a single crystal of dimedone is isolated from the surrounding 1H spins.
Theoretical Auger spectra of the glycine ion in solution
Authors: Liegener C.-M. , Bakhshi A. K. , Chen Runsheng , Ladik J.
Published: July 2002

The Auger spectra of the glycine zwitterion in aqueous solution have been calculated by a Green’s function method. The hydration shell has been simulated by point charges representing the water molecules. The positions of the point charges have been determined by a combination of Monte Carlo and mutually consistent-field calculations. The Auger spectra of the hydrated ion have been compared to the Auger spectra of the free glycine ion and the free glycine molecule. Considerable charge redistributions manifest themselves in the spectra, going from the molecule to the ion mainly in the nitrogen and oxygen spectra. Upon hydration the changes are strongest in the carbon and oxygen spectra.
Experimental determination of CH-stretching–bending–bending cubic force constants of ethane from Raman intensity analysis
Authors: Domingo C. , Montero S.
Published: July 2002

The vibrational anharmonicity of ethane has been experimentally investigated by means of a joint analysis of the gas-phase mean polarizability Raman scattering cross sections and the wave numbers of the multiple vibrational resonances in the C–H or C–D stretching region of several isotopic derivatives. Thirty nine cubic force constants krst in the representation of normal coordinates were obtained in a first step. In a second step they were reduced to a smaller set of isotopically invariant cubic constants Fijk in the representation of curvilinear symmetry coordinates.
Dynamic multiple scattering theory of the Huggins coefficient for discrete Gaussian chains. I. Formal derivation of the full frequency dependence
Authors: Perico Angelo , Freed Karl F.
Published: July 2002

The Huggins coefficient of discrete Gaussian chains is derived from the friction coefficient density tensor to second order in concentration and is formally obtained as a full dynamic multiple scattering expansion. One contribution to the dynamical Huggins coefficient emerges from the single chain term in the multiple scattering expansion, but includes the concentration dependence of the Langevin polymer dynamics to first order in concentration. The other contribution is from the two-polymer multiple scattering term evaluated for the infinite dilution limit dynamics of these two chains. The discrete dynamical multiple scattering theory includes the full dynamics of the interbead scattering factors and therefore enables us to calculate the full frequency dependence of the Huggins coefficient as well as its steady state limit. These quantities are explicitly represented in terms of the single chain Rouse and Zimm eigenvalues and the transformation to Rouse–Zimm normal modes. Numerical evaluations and comparisons with experiment are presented in the accompanying paper.
Translational correlation function of interaction-induced dipoles in dense media
Authors: Gburski Zygmunt , Samios Jannis , Dorfmüller Thomas
Published: July 2002

The time-correlation functions associated with the translational motions of the dipole—induced by permanent multipoles of an arbitrary order 1=1,2,3,...—in a dense fluid have been calculated analytically assuming the isotropic diffusion mechanism. The correlation functions obtained from this model have been compared with the available results of the molecular dynamics simulations in liquid N2 (T=75.5 K, ρ=0.814 g cm−3) and CS2(T=298 K, ρ=1.26 g cm−3) and appear to reflect the proper time scale of the relaxation process.
The asymptotic dispersion of particles in N-layer systems: Periodic boundary conditions
Authors: Mazo Robert M. , Van den Broeck Christian
Published: July 2002

Previous work on dispersion of particles in N-layer systems (generalized Taylor dispersion) for reflecting boundaries is extended to the case of periodic boundary conditions. An explicit expression for the dispersion is presented; this is never greater than the dispersion for the corresponding system with reflecting boundaries. Applications to chromatography with chemical reaction and to anomalous diffusion are made.
Field strength dependence of the electric birefringence of rigid and nonrigid molecules
Authors: Yoshioka Koshiro
Published: July 2002

The field strength dependence of the electric birefringence for a system of noninteracting rigid or nonrigid molecules is calculated on the basis of the most general model, following the formalism of Nagai and Ishikawa. The results are expressed as power series of the field strength. Simple equations are obtained in the cases of permanent dipole orientation and induced dipole orientation. Applications to 1,2-dichloroethane and the nonrigid trumbell model are presented as examples.
An electron-impact spectroscopy investigation of CH3 and some of its pyrolytic precursors
Authors: Walzl K. N. , Koerting C. F. , Xavier I. M. , Kuppermann A.
Published: July 2002

The electronic spectrum of the methyl radical CH3 was investigated by the technique of variable-angle electron energy-loss spectroscopy. By means of pyrolytic decomposition three possible sources of this radical were tried (tetramethyl tin, ethyl nitrite, and di-t-butyl-peroxide). The spectra of these precursors were obtained. Using di-t-butyl-peroxide, relative differential cross sections for the lowest allowed A″2 3s Rydberg transition in CH3 (5.73 eV) were determined at incident energies of 50 and 25 eV. The behavior of the differential cross section for this band is analogous to that of a spin-allowed transition in a closed shell system and, as expected, in the vicinity of this band no transition of a spin-forbidden nature is detected.
A new semiclassical formulation for molecular line broadening
Authors: Bonamy Jeanine , Jolicard Georges
Published: July 2002

An original infinite order method to calculate line broadening is proposed using projection operator algebra and the Linked Cluster Theorem. The S matrix elements are calculated iteratively at any order of perturbation theory. A first application to the O→2H2–Ar rotational line is performed.
X-ray diffraction study of AgX–Ag2O–B2O3 (X=Br,Cl) vitreous electrolytes
Authors: Musinu A. , Paschina G. , Piccaluga G. , Villa M.
Published: July 2002

X-ray diffraction measurements have been performed on glasses of the AgX–Ag2O–B2O3 (X=Br,Cl) systems. The only meaningful structural detail of the radial distribution functions is due to Ag–X interactions. The mean numbers of Ag–X contacts has been obtained through analysis of the high-angle partial structure functions si(s), calculated by subtracting experimental structure function of the Ag2O–B2O3 glasses from that of the corresponding AgX–doped glasses. Calculations have been also performed for AgI–Ag2O–B2O3 glasses, and comparison between the results from systems containing different halides is made. The average number of Ag–X contacts is very similar in samples at equimolar composition, thus suggesting a close structural feature in AgX–doped glasses.
Tests of approximations for inelastic molecule–surface scattering dynamics
Authors: Diestler Dennis J. , Riley Merle E.
Published: July 2002

Any classical dynamical simulation of atom– or molecule–surface scattering is subject to the approximation of truncating the many-body description of the solid to that of a tractable number of atoms (the P zone). This truncation should have no significant effect on the collision dynamics, e.g., the accommodation coefficients and sticking probabilities, for the situation of interest. No ab initio tests of the accuracy of the few existing approximate treatments of gas–surface scattering appear to have been reported. In this work we review the existing approximations and introduce three new ones. One of the three new ones, the weak-coupling approximation, assumes the solid atoms tend to respond independently to the incident molecule; another, the bond-corrected Debye approximation, is a simple modification of the Adelman–Doll damping theory; the third, the outgoing wave approximation, treats the solid as an elastic continuum, in which the wave-like disturbance created by the collision is propagated outwardly from an epicenter near the point of impact. In all, six different approximations are applied to a collision system (adatom interacting via a Morse potential with the simple-cubic Rosenstock–Newell lattice at 0 K) for which numerically exact scattering data (energy accommodation coefficients) are available. Figures of merit are assigned to each approximation over a wide range of collisional parameters. The new outgoing wave approximation is consistently of the highest quality. The results are very encouraging for the easy application of reliable approximations to P zones with only a few atoms
Study of low-energy electron attachment to 1,1,1-C2Cl3F3 using K(n
d) Rydberg atoms
Authors: Johnson C. B. , Walter C. W. , Kalamarides A. , Smith K. A. , Dunning F. B.
Published: July 2002

Studies of K(nd) Rydberg atom collisions (10≤n≤100) are used to investigate electron attachment to trichlorotrifluoroethane 1,1,1-C2Cl3F3 (TCTFE) at subthermal energies. The Rydberg atom data indicate that electron attachment to TCTFE occurs predominantly through dissociative capture and that the cross section for this process is large. Differences between the present results and those obtained using the threshold photoelectron spectroscopy (TPSA) technique are discussed.
Free radicals formed by reaction of germane with hydrogen atoms in xenon matrix at very low temperatures
Authors: Nakamura K. , Masaki N. , Okamoto M. , Sato S. , Shimokoshi K.
Published: July 2002

The radicals formed by the reaction of GeH4 with H in the Xe matrix were investigated by electron spin resonance (ESR) spectroscopy at very low temperatures. The radicals observed were identified as GeH3 and GeH5. The newly observed radical GeH5 is considered as the intermediate of the reaction H+GeH4→H2+GeH3. The ESR parameters of these radicals were determined by numerical deconvolution of the observed spectra.
Photofragments of Ni(CO)4: A linear combination of Gaussian-type orbitals (LCGTO) Xα study
Authors: Rösch Notker , Jörg Harald , Kotzian Manfred
Published: July 2002

The photolytic reaction of Ni(CO)4 upon UV irradiation has been studied theoretically using the LCGTO-Xα method. The origin of the observed luminescence is assigned to emission from the charge–transfer excited fragment Ni(CO)3 based on an analysis of the involved orbitals and on total energy calculations. The theoretical results are able to explain the width of the experimental emission spectrum quantitatively, but overestimate somewhat the corresponding excitation energies. It is shown that the fragment Ni(CO)3 itself may undergo a related photolytic reaction although a high density of excited states and reduced symmetry allow several reaction paths for the dissociation of one further metal–ligand bond.
Curvilinear coordinate formulation for vibration–rotation–large amplitude internal motion interactions. II. Application to the water molecule
Authors: Guan Yuhua , Quade C. Richard
Published: July 2002

The vibration–rotation–large amplitude internal motion (LAM) interaction theory developed in the previous paper, hereby referred to as I, is now applied to calculate the vibration–rotation energy levels of the water molecule treating the bending mode as the LAM. Fourier sine functions are used as the basis for the bending mode, harmonic oscillator functions for the two stretching modes, and Wang functions for the rotational motion. Using the Hoy–Mills–Strey (HMS) and Hoy–Bunker (HB) force constants and molecular geometry, the vibration–rotation–LAM energy levels have been calculated from nτ=0 to 2 for the bending mode and from J=0 to 10 for the rotational motion, as well as for the first excited states of the stretching modes. A revised set of force constants, referred to as the Guan–Quade (GQ) force constants, have been determined which fit the vibrational data substantially better and fit the rotational data in some cases better and in all respects at least as well as the HB force constants. In all cases the GQ and HB force constants give a better fit to the observed rotational data than the HMS force constants.
The effects of site exchange on the ESR spectra of free radicals with radical pair mechanism chemically induced dynamic electron polarization (CIDEP)
Authors: McLauchlan K. A. , Stevens D. G.
Published: July 2002

The possible effects of exchange processes upon polarized ESR spectra are discussed using the amended Bloch equations. The results are applied to an analysis of the polarized ESR spectrum of the cyclohex-1-olyl radical, observed over a range of temperatures using the time integration spectroscopy technique. The spectrum obtained at 223 K displays an unusual E/A/E/A polarization pattern, the full analysis of which is given. In the light of these results, the fact that the polarized ESR spectra of radical anions usually fail to show any radical pair mechanism polarization is discussed.
An exact solution of the van der Waals interaction between two ground-state hydrogen atoms. III
Authors: Koga Toshikatsu , Uchiyama Takeshi , Uji-ie Mitsuru
Published: July 2002

To supplement our previous work on the nonvariational momentum-space solution of the H(1s)–H(1s) van der Waals interaction, accuracy of the solution is examined through the local energy of the leading perturbation wave function in momentum and position spaces. The result shows that the local energies are angular independent in both spaces and the angular part of the wave function has a correct form. The radial dependence of the local energies diminishes rapidly with the increasing number of expansion terms, which demonstrates high accuracy of the wave function obtained by the momentum-space technique. The wave function is also shown to satisfy the zero momentum and zero potential energy criteria.
Diffusion in the two-dimensional nonoverlapping Lorentz gas
Authors: James Corinne P. , Evans Glenn T.
Published: July 2002

The self-diffusion coefficient, velocity autocorrelation function, and distribution of collision times for a two-dimensional nonoverlapping Lorentz gas were calculated using molecular dynamics simulation. The systems studied covered a range of densities, from a packing fraction (πNr2/L2) of 0.01 to 0.8. Self-diffusion coefficients were found to agree to all densities with kinetic theory predictions [A. Weijland and J. M. J. van Leeuwen, Physica 38, 35 (1968)] if the radial distribution function (rdf) was taken into account. The density dependence of the decay of the velocity autocorrelation function was qualitatively different from that predicted by kinetic theory. The distribution of collision times was nearly exponential for all but the highest density studied.
A theoretical study of chemisorption sites for oxygen on the NbC(100) surface
Authors: Orita Masahiro , Kojima Isao , Miyazaki Eizo
Published: July 2002

Theoretical calculations using the DV-Xα-MO method have been performed for various clusters to investigate the chemisorption site of oxygen on the NbC(100) surface. The electronic edge effects arising from the use of the cluster model were found to be small when the total local density of states (LDOS) curve for a surface atom surrounded by all of their nearest-neighbor atoms was compared with ultraviolet photoelectron spectroscopy (UPS) spectrum. It was found that an oxygen chemisorbed on such a surrounded carbon atom created stable covalent bonds with neighboring niobium atoms as well as the carbon atom, and that the LDOS difference curve of the carbon on-top model was in good agreement with UPS difference spectrum of oxygen adsorbed on a NbC(100) surface. However, the oxygen adsorbed on the niobium atom was unstable, and the calculated LDOS curve was not in agreement with the experimental UPS spectrum.
Deconvoluting the visible absorption spectrum of methyl orange using inverse Raman transform techniques
Authors: Rava Richard P.
Published: July 2002

Resonance Raman excitation profiles have been measured for all the active vibrations between 800 and 1600 cm−1 over the visible absorption band of methyl orange. The excitation profiles indicate that two transitions contribute to the observed absorption band profile, and that individual vibrations appear to be enhanced via resonance with single electronic transitions. Using inverse Raman transform techniques, the absorption bands responsible for the resonance Raman activity are determined from the excitation profiles of the 924 and 1393 cm−1 modes. Two distinct absorption bands with maxima at 437 and 475 nm are found to fit the excitation profiles and inverse transform results. The transitions responsible for these bands are determined from qualitative molecular orbital arguments and are assigned to nπ* and charge transfer excitations.
Electron degradation and yields of initial products. I. Excited species generated by electrons in binary mixtures
Authors: Kimura Mineo , Inokuti Mitio
Published: July 2002

Initial yields of excited species resulting from electron degradation in Ar+H2 mixtures have been calculated using the Fowler equation. Following up the previous study of yields of ions by Eggarter [J. Chem. Physl 84, 6123 (1986)] and by Inokuti and Eggarter [J. Chem. Phys. 86, 3870 (1987)], the present work treats initial yields of excited species over the entire range of the composition of Ar+H2 mixtures. The variation of the yield with the composition depends on the kind of excited species. The most noteworthy of the results obtained concerns the Ar metastable-state yield, which shows peculiar behavior when a small amount of H2 is introduced in the media.
The effect of OH rotation on the reaction OH(v=0, j)+H2→H2O+H
Authors: Harrison Judith A. , Mayne Howard R.
Published: July 2002

The reaction cross section for OH(v=0, j≤31)+H2→H2O+H has been calculated using quasiclassical trajectories at E=0.15, 0.20, and 0.30 eV. There is an initial increase in reactivity with j, probably due to long-range R→T transfer. At very high j, the cross section decreases, probably because of disruption of the transition state by the OH rotation.
The electronic spectrum of s-tetrazine: Structures and vibrational frequencies of the ground and excited electronic states
Authors: Scheiner Andrew C. , Schaefer Henry F.
Published: July 2002

The ground and excited electronic states of the s-tetrazine molecule have been studied using the methods of ab initio electronic structure theory. In particular, complete self-consistent field (SCF) optimizations of the equilibrium structures on the X̃ 1Ag, ã 3B3u, and Ã 1Au(C2h)/1B3u (D2h) surfaces using both double-ζ (DZ) and DZ+polarization (DZ+P) basis sets have been carried out. Harmonic vibrational frequencies have been analytically evaluated at these stationary points. DZ SCF results for higher excited electronic states are also reported with the optimizations on these surfaces having been restricted to D2h symmetry. Single point configuration interaction energies including single and double excitations relative to the SCF references (CISD) have been used to predict both vertical and adiabatic electronic excitation energies for all states investigated herein. In addition the Davidson correction [CISD(+Q)] and the closed shell coupled cluster singles and doubles (CCSD) method have been used to approximate the effect of higher excitations. Our results for the equilibrium geometries, harmonic vibrational frequencies, electronic excitation energies, and the energies of the photodissociation of s-tetrazine are analyzed and compared to spectroscopic results where available.
Spectroscopic observation of the highest vibrational level of the HD+(2Σ+) molecule
Authors: Carrington Alan , McNab Iain R. , Montgomerie Christine A.
Published: July 2002

Spectroscopic observation of the highest vibrational level of HD+(v=21) in its ground electronic state is reported. Calculations of constants from the resolved hyperfine structure allow unambiguous determination of the Fermi contact parameters for the levels 17,1 and 21,0, showing that in the level 21,0 the electron distribution is asymmetric toward the lower dissociation limit H++D, with an average electron density of 0.094 at the proton and 0.902 at the deuteron.
Far infrared spectra of the tetrahydrocarbons CBr4 and CCl4
Authors: Vij J. K.
Published: July 2002

Far infrared spectra of carbon tetrabromide in solutions of carbon tetrachloride has been measured at 20 °C in the wave number range 15–250 cm−1. The apparent dipole moments for CCl4 and CBr4 have been calculated as 0.15 and 0.31 D, respectively, on the assumption that the apparent dipole moment arises entirely from the octopole moment (Ω) of the neighboring molecules. Ω for CCl4 and CBr4 has been determined to be (13±1)×10−34 and (18±3)×10−34 esu, respectively. These values agree closely with those estimated from transition temperatures in solids composed of these molecules.
Structural relaxation time and rigidity of deionized suspensions of monodisperse polystyrene latex spheres
Authors: Okubo Tsuneo
Published: July 2002

Structural relaxation time (τ) of ordered structures is observed for the first time by the spectrophotometric and conductance stopped-flow techniques for deionized polystyrene latex spheres (35–500 nm in diameter), for which the distributions are both ‘‘crystal-like’’ and ‘‘liquid-like.’’ Two kinds of τ values, fast (τf) and slow steps, are observed. The τf values decrease with latex concentration. Theoretical values for τf, calculated using the translational diffusion constants of the latex spheres evaluated by the Einstein–Stokes equation, agree very well with the observed τf values for the strongly interacting colloids. The results support the hypothesis that electrostatic intersphere repulsion is essential to explain the dynamic properties of the spheres. The effective diameter of the spheres must include the Debye-screening length. The rigidity of the deionized and crystal-like latex suspension, which is estimated from the τf values, ranges from 0.005 to 10 dyn cm−2, and increases as the concentration and the charge density of the spheres increase and/or the size decreases.
Cross sections for rotationally inelastic scattering of formaldehyde. III. Differential measurements on D2CO–H2 scattering
Authors: van Hulst Niko F. , ter Meulen J. J. , Dymanus A.
Published: July 2002

Differential cross sections for rotational transitions in D2CO induced by collisions with H2 are measured at a collision energy of 17 meV. The 110 state of D2CO is prepared with high state purity by a combination of rotational cooling in a seeded beam expansion and electrostatic state selection. The final state after scattering is probed as a function of the scattering angle by laser-induced fluorescence detection with excitation at 325 nm. The first results with the final states 110, 111, 211, and 212 are presented. The differential cross section for the ΔJ=1 transition 110→211 displays a relatively large contribution at large angles compared to the cross sections for the other transitions.
Novel a
b i
n
i
t
i
o self-consistent-field approach to molecular solids under pressure. II. Solid H2 under high pressure
Authors: Raynor Susanne
Published: July 2002

As a test of our new ab initio approach to the study of molecular solids under pressure, the PV relations for solid H2 under high pressure were studied. Using a minimum basis set of Slater orbitals and a single determinant crystal wave function, we found the hexagonal closest packed structure to be more stable than the face-centered cubic, body-centered cubic, or Pa3 structures investigated. Structurally optimized calculations of the PV isotherm at 0 K for the hexagonal closest packed solid gave excellent agreement with extrapolated experimental data. Furthermore, the calculated vibron frequency shows an initial increase with increasing pressure followed by a decrease beginning at ∼0.5 Mbars, as has been previously seen experimentally.
The c
i
s influence of bromine in SF5Br. A combined electron diffraction–microwave study
Authors: Christen Dines , Mack Hans-Georg , Oberhammer Heinz
Published: July 2002

The gas phase molecular structure of SF5Br has been determined by electron diffraction and by joint analyses, including rotational constants of only one isotopic species (32S79Br or32S81Br, respectively). The following parameters (rz values with 2σ uncertainties) were derived in the joint analyses: S–Fe=1.671(2), S–Fa=1.560(6), S–Br=2.232(2) Å and FeSFa=89.3(1)°. These results demonstrate a small cis influence of Br on the SF5 group, i.e., the equatorial bonds (cis to Br) are affected more strongly by the substituent than is the axial bond. Ab initio calculations for SF6 and HSF5 with various basis sets (3-21G, 3-21G*, and 6-31G*) confirm the cis influence of a σ-donating substituent and allow for a qualitative interpretation of the substituent effects. The microwave spectrum has been recorded in the range of the J=28–29 transitions and the ground state transition of the 34S isotopic species has been reassigned (B0=1169.54 MHz for 34S79Br and 1157.10 MHz for 34S81Br). Test calculations demonstrate that geometric parameters derived from spectroscopic data alone (rotational constants and centrifugal distortion constant R6) are highly sensitive to isotopic differences and to the force field used in the calculation of R6.