bluuebunny/crossref_metadata_2025 huggingface dataset:
Ozone photolysis: A determination of the electronic and vibrational state distributions of primary products
Authors: Sparks R. K. , Carlson L. R. , Shobatake K. , Kowalczyk M. L. , Lee Y. T.
Published: February 2003

A high resolution molecular beam measurement of the energy spectra of O3 photolysis products was performed at 266 nm. (AIP)
Experimental confirmation of the Jahn–Teller distortion of CH4+
Authors: Gemmell Donald S. , Kanter Elliot P. , Pietsch Werner J.
Published: February 2003

We report measured energy and angular distributions for H+ and Cn+ (n=2,3,4) fragments resulting from the collisional dissociation of 194 keV/amu Chn+ (n=0–4) in thin carbon foils. From the systematic trends of these ’’Coulomb explosion’’ spectra, one can obtain qualitative information on the structures of these species. In particular, the series displays a narrowing of the carbon angular and energy widths as protons are symmetrically added around a central carbon atom and provide a ’’focusing’’ effect. Because of the Jahn–Teller distortion, the widths measured for CH4+ are dramatically increased. (AIP)
A new method for observing the rotational spectra of weak molecular complexes: KrHCl
Authors: Balle T. J. , Campbell E. J. , Keenan M. R. , Flygare W. H.
Published: February 2003

A new method of observing the rotational transitions of weak molecular complexes by combining the techniques of microwave Fourier transform spectroscopy, a Fabry–Perot cavity, and a pulsed nozzle source of molecules is described. High resolution and good sensitivity are achieved. Twelve isotopic species of the KrHCl molecule involving all combinations of the 86Kr, 84Kr, 82Kr, H, D, 35Cl, and 37Cl isotopes are assigned and the rotational constants, Cl nuclear quadrupole coupling constants, and centrifugal distortion constants are all given. The molecular structure indicates a linear equilibrium structure with the H(D) atom between the Kr and Cl atoms. However, the inverse moments of inertia measured here indicate large amplitude vibrations of the H(D) atom relative to the Kr–Cl internuclear line. Estimates of the Kr–Cl stretching frequency and force constants, which show considerable dependence on the isotopic species, are also given. Bending frequencies and force constants are also given.
Glass transition in a soft-sphere model
Authors: Cape J. Neil , Woodcock Leslie V.
Published: February 2003

A molecular dynamics study of the glass forming properties of the inverse-twelfth-power soft-sphere model is reported. MD results in the equilibrium range for N=4000 are used to parametrize a six-term virial equation for the fluid and a three term anharmonic perturbation equation-of-state for the crystal, and thereby determine the excess entropy of the supercooled fluid. The hypothetical Kauzmann catastrophe temperature (Tk) of the extrapolated supercooled fluid corresponding to zero excess entropy is thus determined. When a 4000-particle system is cooled at a rate approximately 60 times slower than has previously been accomplished there is no evidence of crystal nucleation. On annealing the supercooled fluid for a very long time nucleation is apparent. The supercooled fluid equation-of-state data is fitted to a polynomial and the variation in heat capacity through the glass transition range is obtained. This yields an operational glass transition temperature Tgk, defined by the onset of kinetic retardation, and a limiting thermodynamic glass transition temperature (To). Both Tgk and To may be also observed from diffusion data and they coincide with those obtained from heat capacities to within the procedural uncertainties. Comparisons are made with the behavior of hard-sphere and Lennard–Jones systems in MD-glass formation. The results are consistent with the postulate of a thermodynamic transition at To, associated with vanishing self-diffusion and a limiting ground-state amorphous solid phase.
Comparison of local-exchange approximations for intermediate-energy electron–molecule differential cross sections
Authors: Onda Kunizo , Truhlar Donald G.
Published: February 2003

Converged rigid-rotator rotational close coupling calculations have been performed for two different effective potentials. The differential cross sections for intermediate energy electron–molecule scattering are calculated. (AIP)
The chemical shift tensor for a strongly hydrogen-bonded proton: The carboxylic proton in KHCH2(COO)2
Authors: Berglund Bo , Carson Douglas G. , Vaughan Robert W.
Published: February 2003

The chemical shift tensor for the carboxylic proton in potassium hydrogen malonate has been determined from a proton multiple pulse experiment carried out at 270 MHz. Both the values of the averaged chemical shift relative to tetramethylsilane (TMS), ?=−20.5 (5) and the chemical anisotropy, Δσ=27.6 (6), are consistent with the very strong hydrogen bond found for the carboxylic proton in KHCH2(COO)2. The directions of the eigenvectors are similar to those found for proton chemical shift tensors determined for other hydrogen-bonded systems, i.e., the z-principal axis is fairly close to the O⋅⋅⋅H⋅⋅⋅O vector off by 9 (2) °, and the x-principal axis is close to the normal of the plane defined by the carboxylic groups [off by 8 (2) °].
Trapping in dilute quasi-one-dimensional systems
Authors: Klafter J. , Silbey R.
Published: February 2003

A model is developed for calculating the asymptotic trapping rate, by a sink, of an excitation migrating in a quasi-one-dimensional dilute system. The asymptotic behavior for the dilute limit differs considerably from that corresponding to a concentrated system. The migration is assumed to be incoherent and is described within the continuous time random walk approach. The competing roles of short range exchange coupling and of long range dipole–dipole coupling is also discussed using time scaling arguments.
Collisional relaxation of low lying electronically excited states of uranium: f3d
s2(5K5) and (5L7)
Authors: Chen Hao-Lin , Borzileri C.
Published: February 2003

Laser induced fluorescence techniques have been used to measure the rates of electronic relaxation of atomic uranium in a beam-gas scattering apparatus. Cross sections for the collisional deactivation of the U f3ds2(5K50) and (5L70) states by H2, D2, HD, CH4, N2, and CO at room temperature are reported. Upper limits for quenching cross sections with He were also obtained. Relaxation of these uranium metastables by molecular hydrogen (H2, D2, and HD) and methane appears to proceed by resonant electronic-to-rotational or electronic-to-vibration/rotational energy transfer processes.
Collisional relaxation of highly excited uranium atoms in gases
Authors: Chen Hao-Lin , Borzileri C.
Published: February 2003

A laser induced fluorescence technique has been used to measure the electronic relaxation rates of highly excited uranium atoms. Cross sections for the collisional deactivation of atomic uranium in the 15 632 and 24 560 cm−1 states by He3, He4, H2, D2, Ne, and CH4 at room temperature are reported. Relaxation of these high lying states by foreign gases is very efficient and is likely governed by an inter-state-mixing process leaving the excited uranium atoms in very close lying neighboring levels.
Statics and dynamics of the freely jointed polymer chain with Lennard-Jones interaction
Authors: Baumgärtner A.
Published: February 2003

Using a dynamic Monte Carlo method we investigated the thermodynamics of static and time-dependent properties of the freely jointed polymer chain with Lennard-Jones type intramolecular forces. The Θ temperture is calculated to kBΘ/−=3.70±0.01 (− is the Lennard-Jones energy parameter). We give estimates for the equilibrium values of end-to-end distances, radii of gyration, and densities for chains consisting of up to N=63 segments and for various temperatures. The detailed structure of the extended coil state (T≳Θ) and the dense globular state (T<Θ) are demonstrated by their average internal distances and their structure functions. The results seem to confirm the predicted scaling laws. Especially we found that for T=Θ the mean size of the coil is ∼N1/2 but the detailed structure is different from a random walk shape. Although the specific heat exhibits a maximum below the Θ temperature, the finite size effects are too serious to confirm the predicted logarithmic divergency. The dynamics of our Monte Carlo method simulate the Rouse model. The density correlation function and the associated relaxation time are calculated. The results are consistent with dynamic scaling predictions. The segment correlation function exhibits the initial ∼t1/2 behavior and the diffusional behavior ∼ t at large times.
Photoassociation, photoluminescence, and collisional dissociation of the Sr2 dimer
Authors: Bergeman T. , Liao P. F.
Published: February 2003

We report observations and analysis of the laser-excited photoluminescence of Sr2. The spectra contains some discrete molecular line spectra, but is dominated by extensive, deeply modulated continua characteristic of bound–free transitions of excimer systems. Dye laser and argon laser excitation of the Sr2 dimer is used. Some of the spectra is attributed to fluorescence from dimers created by laser induced photoassociation of free Sr atoms. Techniques are developed to obtain Morse potential parameters by computer modeling of the observed spectra. We find for the X 1Σ+g state, De=1100±100 cm−1, ωe=39.6±1 cm−1; for the A 1Σ+u state, De=5460±100 cm−1, ωe=83±3 cm−1; and Re″−Re′=0.49±0.02 Å. Strong collision-induced predissociation is observed and attributed to a potential curve crossing. Cross sections for dissociation by argon are reported as a function of laser excitation wavelength.
Laser-induced fluorescence study of the reactions of F atoms with CH3I and CF3I
Authors: Stein L. , Wanner J. , Walther H.
Published: February 2003

The internal vibrational and rotational product state distributions of IF formed in the reactions of F+CH3I→IF+CH3 and F+CH3I→IF+CF3 have been measured with the laser-induced fluorescence method employing cw dye lasers. The experiments have been performed with crossed molecular beams at a relative collision energy of ∼7 kJ mol−1. The mean fraction of Etot entering product vibration and rotation has been determined to be 〈f′V〉=0.15±0.02; 〈f'R〉=0.14±0.03 for F+CH3I; and 〈f′V〉=0.11±0.02; 〈f′R〉=0.10±0.02 for F+CF3I. From the comparison of the fluorescence intensities the ratio of the total average cross sections of the two reactions has been determined to be σtot (CF3I)/σtot (CH3I) =2.2±0.5. The vibrational and rotational product state distributions are essentially statistical indicating that the reactions proceed through a long-lived complex. Our data support Farrar and Lee’s interpretation of the IF angular and velocity distribution measurement for the reaction F+CH3I at a similar collision energy [J. Chem. Phys. 63, 3639 (1975)]. From the data of the two independent measurements the average amount of the internal excitation of the CH3 radical may be estimated to 〈f′int (CH3) ≳∼0.4. The smaller amount of IF product excitation in case of the reaction F+CF3I suggests that even a larger fraction of Etot is channeled into internal excitation of the CF3 radical.
Analytic theory of extrema. IV. Relaxation from metastable and unstable states
Authors: West Bruce J. , Lindenberg Katja , Seshadri V.
Published: February 2003

The exact and asymptotic results for mean first passage times of master equation processes obtained in the companion paper are here applied to the study of relaxation times from metastable and unstable states. It is shown that the use of a master equation necessarily leads to an exponential system size dependence of the relaxation time from a metastable state. It is also a general consequence of the structure of the master equation that the relaxation from an unstable state occurs on a much shorter time scale than from a metastable state.
Collision dynamics of intermode energy flow in laser pumped polyatomic molecules: CH3F
Authors: Sheorey Rekha Sapre , Flynn George
Published: February 2003

Subsequent to placing excess vibrational population in the ν3C–F stretching mode of CH3F by a Q-switched CO2 laser, the time dependence of fluorescence signals from the overtone level 2ν3 and from all other vibrational fundamental levels has been monitored and analyzed. The nearly resonant, ladder climbing process CH3F(ν3)+CH3F(ν3) ⇄CH3F(2ν3)+CH3F(O)+18 cm−1 reaches steady state in about 3.3 gas kinetic collisions. The excess vibrational energy contained in the ν3 mode is transferred to the remaining CH3F modes on a longer timescale. Direct coupling exists between ν3 and ν6 and between ν6 and ν2,ν5: CH3F(ν3)+CH3F⇄CH3F(ν6)+CH3F−133 cm−1 CH3F(ν6)+CH3F⇄CH3F(ν2,ν5)+CH3F−284 cm−1. These two processes have been found to reach steady state in 30 and 120 gas kinetic collisions, respectively, in pure CH3F. No evidence for the direct coupling between ν3 and ν2,ν5 has been found. Equilibration of the C–H stretch levels ν1, ν4 with the rest of the CH3F vibrational levels via the fairly efficient ladder climbing process 2CH3F(ν2,ν5) ⇄CH3F(2ν2,2ν5)+CH3F(O)+87 cm−1 which populates the overtones 2ν2,2ν5, followed by crossover between the Fermi mixed levels 2ν5 and ν1 CH3F(2ν5)+CH3F⇄CH3F(ν1)+CH3F is consistent with the data obtained in the present experiments.
Energy localization in substitutionally disordered solids. II. Studies by optical and optically detected magnetic resonance spectroscopy
Authors: Smith D. D. , Millar D. P. , Zewail A. H.
Published: February 2003

In continuation of previous work, we present experimental measurements on the localization of triplet Frenkel excitons in isotopically doped phenazine and 1,4-dibromonaphthalene (2-D and 1-D effective excitation transfer topology, respectively). Dependence of steady state impurity aggregate (monomer, dimers, etc.) emission intensities on temperature, concentration of dopant, and the dimensionality is experimentally measured and theoretically modeled. Effects of phonons and excited state lifetimes are explicitly included in a numerical simulation of the data by average-lattice rate equations. The rate equations explain the major features of the experimental data quite well. For use in the rate equations, we have performed Monte Carlo experiments to determine cluster probabilities on 1-D and anisotropic 2-D lattices. Finally, the relevance of these findings to Anderson localization and percolation theory is discussed.
The liquid–solid transition of the hard sphere system from uniformity of the chemical potential
Authors: Robledo Alberto
Published: February 2003

The search for solidlike singlet distribution functions in a system of hard spheres is undertaken. The analysis is based on the potential-distribution theory for nonuniform fluids. The ensuing requirement of constancy of the chemical potential throughout the system leads to a nonlinear integro-difference equation for the singlet density which is exact in one dimension. Bifurcations from its uniform solution, occurring before close packing and of an oscillatory nature, are found for both hard disks and hard spheres, but not for hard rods. The branching solution for hard spheres has the symmetry of a hexagonal close packing lattice, whereas that for hard disks is triangular. An investigation is also made of the stability of the fluid states. It is found that fluid instabilities and bifurcation points appear simultaneously.
Quadrupolar double transitions S1(J)+S(J) in the infrared fundamental band of molecular hydrogen at 77 K
Authors: Sen A. , Prasad R. D. G. , Reddy S. Paddi
Published: February 2003

Double transitions S1(J)+S0(J) corresponding to the vibrational–rotational transition in one molecule and a rotational transition in the other molecule, occurring simultaneously in a colliding pair, have been observed in the infrared fundamental band of normal H2 at 77 K for gas densities in the range 100–320 amagat with a 2 m absorption cell. These transitions arise because of the contribution to the intermolecular interaction by the anisotropic component of the polarizability of one molecule in the quadrupole field of the other and occur in the high wave number tail of the S1(J) and Q1(J)+S0(J) components of the band. The experimental profiles were analyzed by assuming appropriate line shape functions and using the theoretical matrix elements of the quadrupole moment, isotropic polarizability, and anisotropy of the polarizability, of the H2 molecule. From this analysis the characteristic half-width parameter δq and the binary and ternary absorption coefficients of the S1(J)+S0(J) transitions have been obtained. The value of δq obtained in the present work is in agreement with the one obtained for the S1(J) and Q1(J)+S0(J) components of the lower density profiles of the band at 77 K reported earlier from our laboratory [S. P. Reddy, G. Varghese, and R. D. G. Prasad, Phys. Rev. A 15, 975 (1977)]. The experimental value of the binary absorption coefficient of S1(1)+S0(1) is 1.3×10−9 cm−1 amagat−2, which is in close agreement with the theoretical value.
The analysis of multisite spectra
Authors: Labhart Martin , Miklos Gabor , Keller Jürg , Wild Urs P.
Published: February 2003

A deconvolution method is presented which allows one to calculate the single site zero-phonon spectrum of a molecule from a conventionally recorded Shpolskii multisite luminescence spectrum. The drastic decrease in the number of quasilines and the slight improvement in resolution significantly contribute to a straightforward analysis of the vibrational structure.
ESR and Mössbauer studies of crystallization process of sodium iron silicate glass
Authors: Komatsu T. , Soga N.
Published: February 2003

ESR and Mössbauer effect measurements in the crystallization process of 5Na2O⋅Fe2O3⋅8SiO2 glass were made to elucidate the state of Fe3+ ions in glass. The ESR spectra in the crystallization process showed the disappearance of the g=4.3 line and the narrowing of linewidth of the absorption line centered at g=2.0. The Mössbauer spectra showed the change from the doublet to the singlet in the crystallization process. These phenomena were interpreted on the basis of the removal of the site distortions of Fe3+ ions in the glass and the removal of randomness in environments of Fe3+ ions in the glass.
Decay dynamics of the CN* (B 2Σ+) and XeF* (B 2Σ+ and C 2Π3/2) states
Authors: Poliakoff E. D. , Southworth S. H. , White M. G. , Thornton G. , Rosenberg R. A. , Shirley D. A.
Published: February 2003

The fluorescence decay of CN* (B 2Σ+) and XeF* (B 2Σ+ and C 2Π3/2) radicals has been investigated following photodissociation of ICN and XeF2, respectively. Pulsed synchrotron radiation from the Stanford Synchrotron Radiation Laboratory was used as an excitation source so that the fluorescence decay could be monitored directly. Pressure-dependent studies were carried out to separate the effects of collisional quenching from those of radiative decay. The radiative lifetimes derived for the CN* (B 2Σ+), XeF* (B 2Σ+), and XeF* (C 2Π3/2) radicals are 70.5±1.6, 14.2±0.2, and 98±10 nsec, respectively. The collisional fluorescence quenching rate for the CN* (B 2Σ+) state by ICN was determined to be (1.15±0.04) ×10−9 cm3 sec−1(294 K). In addition to the CN* (B 2Σ+) fluorescence observed from ICN excitation, a very fast fluorescence component was observed which is attributed to radiative decay of valence (and/or Rydberg) excitations in ICN.
Absolute rate constant for the reaction of O(3P) with CH3SCH3 from 272 to 472 K
Authors: Lee J. H. , Tang I. N. , Klemm R. B.
Published: February 2003

Rate constants for the oxidation reactions of organic sulfur compounds have become increasingly important due to their potential role in the formation of tropospheric and stratospheric sulfate aerosols. The present study deals with the reaction of the ground state oxygen atom with dimethyl sulfide. A discharge fast flow–resonance fluorescence technique was used to follow the decay of O(3P) atoms in the presence of excess CH3SCH3 under pseudo-first-order conditions. Kinetic data, obtained over the temperature range 272 to 472 K, are well represented by the Arrhenius expression, kbi= (1.28±0.12) ×10−11 exp[(803±60)/RT] cm3 molecule−1 sec−1. The results are compared to those of previous studies which employed different experimental techniques.
Depletion layer studies in organic films: Temperature dependence studies of low frequency capacitance measurements in tetracene and magnesium phthalocyanine
Authors: Twarowski Allen J. , Albrecht A. C.
Published: February 2003

The voltage dependence of capacitance in two photovoltaic sandwich cells, (Al ‖ tetracene ‖ Nesatron) and (Al ‖ magnesium phthalocyanine ‖ Nesatron), is reported as a function of temperature. The tetracene cell shows a voltage independent (geometric) capacitance at room temperature which upon heating to 120 °C changes to a depletion layer type capacitance at 10−1 Hz. Values for depletion width, carrier concentration, and barrier voltage are consistent with those reported in a previous publication where carriers in tetracene were mobilized by light. Magnesium phthalocyanine cells, on the other hand, show a depletion layer capacitance at room temperature and upon cooling revert to a geometric capacitance at some lower temperature depending on the frequency of the measurement. A theoretical treatment is presented which describes the frequency and temperature dependence of the depletion layer capacitance. From this analysis a method for measuring activation energies and rate constants for detrapping is obtained. This method is demonstrated for magnesium phthalocyanine cells.
The luminescence of uranium-activated tungstates and molybdates with scheelite structure
Authors: ’t Lam R. U. E. , Blasse G.
Published: February 2003

The luminescence properties of scheelites with composition AWO4–U and AMoO4–U (A=Ca, Sr, or Ba) are reported. The red luminescence is due to a tetrahedral UO2−4 group. There is a strong vibronic coupling with low-frequency vibrational modes. Further the frequency of the symmetric and asymmetric stretching vibrations of the UO2−4 tetrahedron have been determined. The dramatic variation of the luminescence quenching temperature with the nature of the A ion is related to the position and the width of higher excited charge-transfer transitions. The radiant decay times are rather short (10–20 μs). Their temperature dependence shows that at least four energy levels are involved in the radiative emission processes. The green luminescence can be ascribed to the presence of a second phase of composition AUO4.
Measurement of ultrasonic relaxation time and mean free path in liquids
Authors: Takagi K. , Negishi K.
Published: February 2003

It is theoretically shown that the mean free path in liquids is determined with the values of vibrational relaxation times in the liquid and gas states, diameter and potential depth of the molecule. Ultrasonic measurements were made to obtain the relaxation time in five liquids, C6H6, C5H5N, C4H4S, C4H4O, and CH2Cl2. With other necessary values obtained experimentally, the mean free path was determined in the five liquids. The result in C6H6 is 1.79 Å, which is in rough agreement with 1.26 Å predicted by the simple cubic cell model, Λ=2(L−σ), L and σ being the mean distance between molecular centers and the diameter, respectively. Further, a correction is introduced to the cell model and the equation is modified as Λ=2L−1.89σ, which yields 1.77 Å showing a better agreement with the experimental value. The ratio of ρτ in liquid to that in gas is found to be very close to 4.2 for these compounds.
Vibrational predissociation in hydrogen bonded complexes
Authors: Ewing George E.
Published: February 2003

A vibrationally excited hydrogen bonded complex, A–H*⋅⋅B, is metastable since the vibrational energy of the A–H* chemical bond exceeds that needed to sever the hydrogen bond. After a time the excited complex spontaneously breaks up and fragments A–H and B are produced. We show that this vibrational predissociation process is inefficient when there is unfavorable Franck–Condon overlap between the vibrational wave functions which characterize the bound complex A–H*⋅⋅⋅B and the wave functions which describe the fragments A–H+B. We also show that the vibrational predissociation process is most efficient when the fragments are produced in rotationally or vibrationally excited states. Analytical expressions are presented which allow numbers for the lifetime of A–H*⋅⋅⋅B to be easily obtained with a hand electronic calculator. These lifetimes are exceedingly sensitive to the parameters which characterize the multidimensional potential surface of the hydrogen bonded complex. Since the surface is poorly understood, the resulting lifetimes have only a qualitative significance. Sample calculations of vibrational predissociation of HF*⋅⋅⋅HF and its isotopes together with figures of potential surfaces, wave functions, and coupling terms serve to illustrate the ideas of this paper.
Laser induced fluorescence study of the deactivation of N*2 by H2O, H2S, and CH4
Authors: Bass H. E. , Hottman Steven D. , Bauer H.-J.
Published: February 2003

By adding a small amount of CO2 to mixtures of N2/H2O, N2/H2S, and N2/CH4, the rate at which nitrogen is vibrationally de-excited by these collision partners at room temperature has been determined. A general theory has been developed which is capable of relating rate constants to fluorescence decay times for a complex energy transfer scheme. Some of the problems involved in deducing rate constants from relaxation times are addressed and it is shown that meaningful rate constants can be determined. The rates of N2* (ν=1) de-excitation by H2O, H2S, and CH4 were found to be 1.0±0.2×105 sec−1 atm−1, 1.1±0.2×106 sec−1 atm−1, and 2.0±0.4×105 sec−1 atm−1, respectively. The rates of CO2* (ν3) de-excitation by H2O, H2S, and CH4 were also measured in the course of the study.
The polarization of pure electric quadrupole transitions in the electronic spectra of molecules
Authors: Riehl James P. , Richardson Frederick S.
Published: February 2003

The polarization properties of electric quadrupole contributions to molecular electronic transitions are examined theoretically. Possible manifestations of these electric quadrupole contributions in various types of polarized absorption and emission spectra are considered in detail. The types of polarized spectra considered are circular dichroism (CD), linear dichroism (LD), circularly polarized luminescence (CPL), linearly polarized luminescence (LPL), magnetic circular dichroism (MCD), magnetic linear dichroism (MLD), magnetic circularly polarized luminescence (MCPL), and magnetic linearly polarized luminescence (MLPL). In emission the possible effects of photoselection and reorientational relaxation are investigated. Calculations are presented for the A2g↔T1g transitions of octahedral (Oh) systems and for the Σ+g↔Πu, Πg, and Δg transitions of homonuclear diatomic molecules (D∞h) under a variety of conditions. The identification and characterization of pure electric quadrupole (electronic) transitions using polarized absorption/emission spectroscopy are discussed.
The Hartree–Fock geometry of ammonia
Authors: Rodwell William R. , Radom Leo
Published: February 2003

Ammonia is one of those small molecules which have been used as ’test cases’ in the development of molecular electronic structure calculations. It is important to characterize the geometry in Hartree-Fock limit. Such a study of the equilibrium geometry of ammonia is reported. (AIP).
Elastic electron scattering. I. Scattering from diatomic potentials
Authors: Kohl D. A. , Arvedson M. M.
Published: February 2003

A method is described for calculating electron scattering cross sections from diatomic molecules. The wave function for the scattered electron is represented by a superposition of atomic scattering functions for the component atoms in the molecule plus correction terms for intramolecular multiple scattering. This formalism is applied to scattering from the nitrogen molecule at incident electron energies of 100 eV to 40 keV. The differential cross sections are consistent with the optical theorem and are smaller than the cross sections calculated in the conventional quasikinematic approximation.
Elastic electron scattering. II. Scattering from polyatomic potentials
Authors: Kohl D. A. , Arvedson M. M.
Published: February 2003

A treatment of intramolecular multiple scattering in diatomic molecules is extended to cover the polyatomic case. The differential cross section is expressed as a sum of two and three atom interactions with the latter depending strongly on the geometrical arrangement. However, an interplay between the multiple scattering amplitudes for each three atom fragment ensures that all symmetry requirements of the entire molecule are satisfied. For illustrative purposes, cross sections for ten keV electrons are calculated for the fragments FF2 and FF3 to demonstrate the detailed character of the multiple scattering corrections.
Diastereoselective formation and symmetry properties of ethane derivatives in the semirigid molecular model
Authors: Meinköhn Dirk
Published: February 2003

For ethane derivatives with both centers chirally substituted it is shown how the chiral discrimination of the intramolecular interactions leads to differing concentrations of diastereomers in thermodynamic equilibrium. For this, the difference of the classical partition integrals of the diastereomers is investigated in the semirigid molecular model. The determinant of the generalized inertia tensor is computed, and it is shown how the full derivation of the difference of the partition integrals is greatly simplified by making use of its algebraic property of being a relative invariant of a certain group H of ligand permutations.
Cation transport in gaseous, critical, and liquid benzene and toluene
Authors: Huang Sam S.-S. , Freeman Gordon R.
Published: February 2003

The mobilities μ+ of cations in the fluids of benzene and toluene are 200–3000 fold lower than those of electrons. However, the variations of the cation mobilities with density and temperature are qualitatively similar to those of electrons, to an unexpected degree. In the liquid phase under its vapor pressure at T/Tc<0.8 the cation mobility in benzene obeys Walden’s rule (μ+∝η−x, x=1.0), but in toluene it does not (x=1.1). The ratio of the diffusion coefficients (cation/solvent molecule) is equal to about 0.25 in toluene and 0.50 in benzene. Near the critical point there is a slight maximum in μ+. The maximum is more marked in the density normalized mobility μ+n; it occurs at n/nc=2.0 in benzene and 1.6 in toluene. The mobilities in the critical fluids are 2.76×10−3 and 2.50×10−3 cm2/V s in benzene and toluene, respectively. In the low density gases the ion scattering cross sections, taken to have the form σv=Aα v−α, display α=1.4 for benzene and 1.5 for toluene. The cross sections, appropriately averaged over the Maxwellian distribution of velocities, have magnitudes similar to those expected from scattering by the r−4 polarization potential, but have a greater than expected value of α. The average ion scattering cross sections are about eightfold greater than the corresponding electron scattering cross sections. The value of μ+n in the coexistence vapor is 6.3×1018 molecule/cm V s in benzene up to n/nc=1.0, and is 6.0×1018 in toluene up to n/nc=0.15. At higher densities in the latter μ+n decreases gently, reaching (μ+n)min=4.4×1018 at n/nc=0.9. The temperature coefficient of μ+ at constant n increases with n up to nc, near the coexistence curve. The increased temperature coefficient is attributed to clustering, but the clusters are small.
Time reversal symmetry for magnetic transitions in rotationally inelastic scattering. I. Exact theory
Authors: Khare V. , Kouri D. J.
Published: February 2003

Time reversal symmetry of exact differential scattering amplitudes for atom–diatom collisions is considered in detail. New stronger symmetries are derived for the amplitude in which the quantization axes for the initial and final rotor states are arbitrary. The general time reversal symmetry relation is then specialized to treat the initial–initial, final–final, ? and ?-helicities and Basel convention amplitudes. A new exact selection rule for Basel amplitudes is obtained. Our results are of importance for a general understanding of magnetic transitions in atom–diatom collisions and also for understanding the CS and IOS approximations for magnetic transitions.
Time reversal symmetry for magnetic transitions in rotationally inelastic scattering. II. Angular momentum decoupling approximations
Authors: Khare V. , Kouri Donald J.
Published: February 2003

The consequences of the generalized microscopic reversibility derived in the preceding paper are considered for the jz-conserving coupled states or centrifugal sudden (CS) and energy sudden (ES) approximations. It is shown that the two most popular choices of the CS parameter ? lead to violation of the generalized microscopic reversibility. However, it is also shown that these two choices of ? play the role of time reversal partners to one another. The simplest choice of the ES parameter k leads to an approximation that preserves the generalized microscopic reversibility.
Calculation of dipole–dipole dispersion coefficients for liquid metals
Authors: Chatterjee Bivabasu
Published: February 2003

Based on simple considerations, the dipole–dipole dispersion coefficients for long-ranged attractive forces in liquid metals are calculated. The derived relation contains parameters such as heat of vaporization and molar volume at 0 K. An analysis of subsequently evaluated van der Waals constants and internal pressure corroborates present estimations. For metals of the same group in the periodic table, the dispersion coefficient is found to be an inverse function of electron density estimated at the boundary of a Wigner–Seitz atomic cell.
Crossed beam study of the reaction H2+ (CO,H) HCO+ from 0.74 to 9.25 eV
Authors: Bilotta R. M. , Preuninger F. N. , Farrar J. M.
Published: February 2003

We present a study of the reaction H+2 (CO,H) HCO+ from 0.74 to 9.25 eV and the reaction H2+ (CO,H2) CO+ at 1.9 eV. The proton transfer dynamics appear to follow the elastic spectator mechanism fairly well in the low energy regime. At higher energies, the cross section drops rapidly and the backward scattered intensity moves to barycentric speeds beyond the stripping limit. At low energies, the HCO+ products are highly excited, with 90% of the available energy in internal excitation. At higher energies beyond the spectator stripping limit, depletion of the most highly internally excited states occurs through dissociation and roughly 50% of the available energy appears in internal excitation. We present a correlation diagram analysis based upon the H2CO+ surfaces of Vaz Pires et al. [J. Chem. Phys. 69, 3242 (1978)]. Low symmetry collisions lead to conical intersections of H2CO+ surfaces in the entrance channel, providing a pathway for formation of ground state products through the ? 2B2 state of H2CO+.
The concept of pressure in density functional theory
Authors: Bartolotti Libero J. , Parr Robert G.
Published: February 2003

Using density functional theory, a prescription is given for determining the internal scalar pressure at a point within an atom or molecule. From this expression for the pressure, a thermodynamic expression for the energy is obtained in terms of the chemical potential of the reference system, forces acting on the system, the internal pressure and an additional component X[ρ]; namely, Here μ0 is the chemical potential in the absence of fields, v is the potential due to nuclei, φ is the potential due to electrons, P is the scalar pressure, and X[ρ] is defined by the formula where T[ρ] and K[ρ] are the exact kinetic energy and exchange–correlation functionals. The functional X[ρ] vanishes as N approaches infinity, or in Thomas–Fermi or Thomas–Fermi–Dirac approximation, yet it is necessary to account for chemical binding.
Radiationless decay of vibronically coupled electronic states. II. Non-Condon effects of nontotally symmetric accepting modes
Authors: Siebrand Willem , Zgierski Marek Z.
Published: February 2003

Radiationless transitions from an optically prepared state to the ground state are studied on a model consisting of three electronic states and three harmonic modes of vibration. One nontotally symmetric mode (the inducing mode) couples the lower excited state to the ground state, another, of different symmetry (the coupling mode) couples the two excited states, and the third mode which is totally symmetric is not involved in vibronic coupling but acts only as an energy-accepting mode. If the vibronic couplings are weak, the system can be solved by the methods of Part I [J. Chem. Phys. 69, 5496 (1978)]. The properties of this model are compared with those of a more general model that permits anharmonic adiabatic potentials. If the energy separation between the excited states is small, the upper excited state affects the decay properties of the lower one through two mechanisms, namely, (i) a frequency change in the coupling mode which improves its efficiency as an accepting mode and (ii) a non-Condon effect of the coupling mode on the transition matrix element of the inducing mode. Mechanism (i) corresponds to the proximity effect discussed by Lim et al., but mechanism (ii) which tends to dominate for small energy separations of the excited states and large energy gaps to the ground state, has not been discussed before. The experimental implications of the latter mechanism are briefly discussed.
Exponential transformation of molecular orbitals: A quadratically convergent SCF procedure. I. General formulation and application to closed-shell ground states
Authors: Douady J. , Ellinger Y. , Subra R. , Levy B.
Published: February 2003

A new formulation is proposed for obtaining the SCF wave functions. It is based on an exponential transformation of spin–orbitals which obviates the use of Lagrangian multipliers. A general method is developed for determining explicit expressions for the successive derivatives of the energy with respect to the new variables. The total energy and the wave function are obtained by an iterative procedure, the convergence of which is shown to be quadratic. The method itself provides information as to the Hartree–Fock stability — or instability — of the SCF solution. The method of exponential transformation of molecular orbitals is applicable to closed-shell systems, as well as to a large variety of open-shell systems. As an illustration of the procedure the results of ab initio calculations for ammonia, methane, formaldehyde, and aziridine are given.
Surface tension of a simple fluid: Many body potential
Authors: Grant Martin , Desai Rashmi C.
Published: February 2003

A general statistical mechanical expression is derived for the surface tension of a fluid with an arbitrary many body interaction potential, which reduces to the Kirkwood–Buff formula under the assumption of pairwise additivity. Sum rules for the inhomogeneous system with the many body potential are also presented. These are then used to show that the general expression for surface tension is formally equivalent to the fluctuation formula due to Yvon, and to a recent correlation function expression of Jhon, Desai, and Dahler.
Molecular anions: The ground and excited states of LiF
Authors: Stevens Walter J.
Published: February 2003

A b initio single configuration self-consistent-field calculations have been carried out for the electronic states of LiF− arising from the Li(2S)+F−(1S) and Li(2P)+F−(1S) asymptotes. The 2Σ+ ground state is found to be stable by 0.35 eV with respect to detachment to form LiF(1Σ)+e−. The excited 2Σ+ and 2Π states are unstable and lie in the continuum of the 1Σ+ neutral. However, stabilized SCF solutions for the excited states have been obtained in an energetic region in which electron scattering resonances have recently been predicted. The possible basis set dependence of this result is discussed. The LiF− states are compared to a lithium atom polarized by a point negative charge.
Stripping and complex formation in the reactive scattering of Cs+ ions with benzyl chloride
Authors: Horvat R. C. , Safron S. A.
Published: February 2003

The reaction of Cs+ with benzyl chloride, Cs++BzCl→CsCl+Bz+ in crossed molecular beams is reported. The reaction seems to occur along an attractive potential energy surface yielding forward scattering products. (AIP)
Diamond force constant reconciliation with crystal elastic constants, Raman frequency, bulk compressibility, and neopentane group frequency assignments
Authors: Wall R. S. , Riter J. R.
Published: February 2003

Using the diagonal stretching force constant Kr as the independant variables and assuming its values in the range 4.0–7.0×105 dyn cm−1 the diamond Raman frequency Vr is calculated for each set of force constans. It is suggested that a value of Kr=5.5×105 dyn cm−1 be adopted. (AIP)
Comment on the electronic structure of small beryllium and magnesium clusters and their anions
Authors: Jordan Kenneth D. , Simons Jack
Published: February 2003

LCAO–MO–SCF calculations are performed on Be and Mg clusters. The calculations show that the bonding in tetrahedral Mg4 and Mg4− is very different than in Be4 and Be4−. (AIP)
Collinear reaction surface for He and ArH+
Authors: Pettitt B. M. , Jacobson Kent , Matcha R. L.
Published: February 2003

An LCAO-SCF ccalculation is presented for the potential energy surface for He and ArH. The calculation was done using contracted gaussian basis sets on a Honeywell 6660 computer using the MOLE quantum chemistry program. (AIP)
Comment on ‘‘Stable limit cycles in a two-component bimolecular reaction system’’
Authors: Tyson John J.
Published: February 2003

Kadas and Othmen’s claim regarding the choice of chemical potential in a two-component bimolecular reaction system is disputed. (AIP)
The molecular electronic structure of the lowest 1Σ+g, 3Σ+u, 1Σ+u, 3Σ+g, 1Πu, 1Πg, 3Πu, and 3Πg states of Na2
Authors: Konowalow Daniel D. , Rosenkrantz Marcy E. , Olson Mark L.
Published: February 2003

The multiconfiguration self-consistent field wave functions and potential energy curves for the lowest lying 1Σ+g, 1Σ+u, 3Σ+g, 3Σ+u, 1Πg, 1Πu, 3Πg, and 3Πu states of Na2 are reported. We find good agreement with recent experimental estimates of the dissociation energies for the 1Σ+g and 1Σ+u states. We find the long range hump in the B 1Πu curve to have its maximum height of 520 cm−1 above the separated atom asymptote at R=6.45±0.1 Å; recent experimental estimates of the height are 474 and 554±120 cm−1.
Long wavelength optical mode frequencies and the Anderson–Gruneisen parameter for alkali halide crystals
Authors: Gupta A. P. , Shanker Jai
Published: February 2003

The relation between long wavelength optical mode frequencies and the Anderson–Gruneisen parameter δ for alkali halides studied by Madan suffers from a mathematical error which is rectified in the present communication. A theoretical analysis of δ is presented adopting six potential functions for the short range repulsion energy. Values of δ and γTO calculated from the Varshni–Shukla potential are found in closest agreement with experimental data.
Rotational Raman intensities and the measured change with internuclear distance of the polarizability anisotropy of H2, D2, N2, O2, and CO
Authors: Asawaroengchai Chamnong , Rosenblatt Gerd M.
Published: February 2003

The relative intensities of O and S branch lines in the v=1←v=0 Stokes Raman spectrum of gaseous H2, D2, N2, O2, and CO have been measured in order to obtain a parameter χ= (α∥−α⊥)e/{re[∂ (α∥−α⊥)/∂r]e}. Values for χ reflect the detailed molecular electronic structure and are needed in various scattering theories and to correct rotational and vibrational–rotational Raman intensities for molecular nonrigidity and vibrational-rotational interaction. The values of χ obtained are +0.38±0.01 (H2), +0.38±0.01 (D2), +0.45±0.09 (N2), +0.23±0.07 (O2), and +0.27±0.13 (CO). By combining the measured values of χ with experimental values for 〈α∥−α⊥〉v=0 in the literature, the following values of the polarizability anisotropy and its first derivative at re are obtained: (α∥−α⊥)e=0.288 (H2), 0.282 (D2), 0.691 (N2), 1.080 (O2), and 0.525 (CO) Å3; [∂ (α∥−α⊥)/∂r]e=1.02 (H2), 1.00 (D2), 1.40 (N2) 3.89 (O2), and 1.72 (CO) Å2. These values are compared with literature theoretical values. Molecular polarizability is an experimentally accessible quantity which reflects in a rather direct way the electronic structure of simple molecules. For this reason the orientational anisotropy of molecular polarizability and its variation with internuclear distance are of fundamental interest in developing understanding of the detailed electronic structure of diatomic molecules. Polarizability anistropies and their derivatives are directly related to both absolute and relative intensities of vibrational and rotational Raman transitions.
Macromolecules in nonhomogeneous velocity gradient fields
Authors: Aubert James H. , Tirrell Matthew
Published: February 2003

Some dilute solution kinetic theory results for bead-spring-type macromolecular models (linearly elastic dumbbell and Rouse) in nonuniform velocity gradient fields are obtained. It is shown that contrary to the homogeneous flow result, in general, a macromolecular solute does not move with the local center-of-mass solvent velocity in a nonhomogeneous flow. This results essentially from a unique coupling between segmental Brownian motion of the macromolecule in the flowfield and the center-of-mass translational diffusion possible only in nonhomogeneous flow. Poiseuille flow between parallel plates and circular Couette flow problems are solved for the dumbbell and some results are obtained for the Rouse model. Migration along streamlines occurs in the Poiseuille flow and migration across streamlines occurs in the Couette flow. Additional energy dissipation results for the Rouse model in Poiseuille flow relative to the simple shear flow case. Nonuniform concentration profiles are calculated in Couette flow by taking the appropriate average of the exact equation for the dumbbell configuration space distribution function.
Quenching of excited Xe* (3P2, 3P1, 1P1) states in a neon–xenon mixture
Authors: Wieme W. , Lenaerts J.
Published: February 2003

The decay of the concentration of metastable Xe* (3P2) in a neon–xenon mixture has been measured using the stationary afterglow technique in the pressure range 0.2–100 Torr, at 295° K. The diffusion coefficient of Xe* (3P2) in neon has been determined as D′0=143(±10) cm2 s−1 at 1 Torr. The reaction rates for collisional quenching of Xe* (3P2) in two-body and three-body collisions have been measured, yielding k1=1.85(±0.31) ×10−16 cm3 molecule−1 s−1 for the two-body process Xe* (3P2) +Ne and k2=1.19(±0.19) ×10−32 cm6 molecule−1 s−1 for the three-body process Xe* (3P2)+Xe+Ne. XeNe* excimers resulting from collisions involving Xe(3P1) states are also observed.
Equilibrium properties of molecular fluid mixtures
Authors: Shukla K. P. , Singh Y.
Published: February 2003

The application of perturbation theory in which all tensor interactions are taken as a perturbation of the central potential to a multicomponent fluid mixture of nonspherical molecules of arbitrary symmetry is considered. The influence of angle-dependent pair interactions arising from permanent electric multipole moments, induced dipole moments, anisotropic dispersion and overlap forces, and three-body nonadditive interactions arising from dispersion and classical electric induction interaction between asymmetric molecules on the Helmholtz free energy, in some cases through the third-order of the perturbation theory, is evaluated. The theory is applied to binary mixtures consisting of (i) a component of spherically symmetric molecules and another of axially symmetric molecules and (ii) both components of axially symmetric molecules. Comparisons with experiments are made for Ar–N2, Ar–O2, Ar–CO, N2–O2 and N2–CO binary mixtures at zero pressure isobar and T=83.82 °K as a function of composition for excess Gibbs free energy and excess enthalpy. Agreement with experiment is very satisfactory for all the systems.