bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorescence spectrum of Mo2 in argon and krypton matrices
Authors: Pellin M. J. , Foosnaes T. , Gruen D. M.
Published: February 2003

The time resolved fluorescence spectra of Mo2 isolated in Ar and Kr matrices at 14 °K are presented. Depending on excitation wavelength, either of two separate vibrational progressions with 475.7 (±4.5) cm−1 spacings can be observed in emission. Similarities between several features in the two emission spectra lead to the conclusion that the progressions arise from Mo2 trapped in two distinct sites, each characterized by its own absorption spectrum. Excitation spectra elucidate the overlapping absorption spectra of the two sites. The measured emission lifetimes are long and not single exponential. In krypton matrices, lifetimes of 0.85 msec from one site and a biexponential emission decay of 0.70 and 1.94 msec from a second site are observed. In argon matrices, 2.1 msec emission decay times in one site and a triexponential decay with components of 2.1, 3.93, and 6.3 msec were measured in a second site. Phonon structure in the well resolved spectra show that the matrix coupling is different for the two matrix sites. Various empirical correlation rules are used to test the validity of ωe as well as to compare it to other experimental quantities for Mo2. These rules indicate a 1.9 Å bond length for Mo2. The fluorescence lifetimes and the large spectral shift of the emission relative to the excitation energy lead to the conclusion that the emission does not emanate from the initially excited level. Instead, the emission appears to come from one of the higher spin multiplicity levels in a dense manifold of states lying at somewhat lower energies than the 1Σu+ level coupled by laser radiation to the 1Σg+ ground state.
A classical determination of vibrationally adiabatic barriers and wells of a collinear potential energy surface
Authors: Pollak Eli
Published: February 2003

A necessary and sufficient condition for the existence of a classical vibrationally adiabatic barrier or well in collinear systems is the existence of periodic orbit dividing surfaces. Knowledge of all pods immediately provides all adiabatic barriers and wells. Furthermore, the classical equation connecting the barriers and wells to the masses and potential energy surface of the system is shown, under mild conditions, to be identical in form to the corresponding quantal equation. The only difference is in the determination of the vibrational state which is obtained by WKB quantization classically. The classical barriers and wells can therefore be used to analyze quantal computations. Such analysis is provided for the hydrogen exchange reaction and the F+HH system. A novel result is the existence of vibrationally adiabatic barriers even where no saddle point exists on the static potential energy surface. These barriers are an outcome of competition between the increase of potential energy and decrease of vibrational force constant along the reaction coordinate. Their existence is therefore of general nature — not limited to the specific structure of a given potential energy surface. The experimental significance of these barriers is discussed. The implications on the use of forward or reverse quasiclassical computations is analyzed. A definite conclusion is that one should not average over initial vibrational action in such calculations.
Crossed-beam chemiluminescent reactions of titanium and vanadium with O2
Authors: Parson J. M. , Geiger L. C. , Conway T. J.
Published: February 2003

Titanium and vanadium have been reacted with O2 under crossed-beam conditions to form the TiO A 3Φ, B 3Π, C 3Δ, and E 3Π states and the VO B 4Π state. By heating and seeding the O2 nozzle beam the Ti reaction has been studied at relative collision energies of 4.0, 7.6, and 13.3 kcal/mol, and the V reaction at 3.9, 6.9, 7.6, and 13.1 kcal/mol. Computer simulations of the spectra yield relative rates for formation of TiO(A) and VO(B) vibrational states, which are slightly more excited than the ’’prior’’ model predictions. Increasing the relative collision energy does increase the production of all the electronically excited states, but the VO B state population does not increase as quickly as expected from the prior model. The dependence of the chemiluminescent signals on the metal source temperature suggests reaction of ground state Ti to form TiO(A), but metastable V to form VO (B).
The reaction of hydrogen atoms with ozone as a source of vibrationally excited OH(X 2πi)v = 9 for kinetic studies
Authors: Finlayson-Pitts B. J. , Kleindienst T. E.
Published: February 2003

The reaction of measured initial concentrations of hydrogen atoms with ozone was used to produce vibrationally excited OH(X 2πi)v?9 in a fast flow discharge system at 1.1±0.1 Torr total pressure in argon at 300±3 °K. The kinetic behavior of the highest vibrational level of OH produced (v = 9) [designated OH(9)] was characterized by a variety of experiments including (1) determination of both its rates of formation and decay under conditions of excess H, as well as excess O3, (2) examination of the effects of added quencher/reactants, and (3) determination of the absolute concentrations of OH(9) using published Einstein A factors. In addition, the change in these concentrations of OH(9) for a given set of initial conditions was examined when the total pressure, nature of the carrier gas, coating of the flow tube walls, and concentration of initial, excess hydrogen atoms were varied. The results of these studies indicate that OH(9) is removed sufficiently rapidly from the system that pseudo-first-order kinetics cannot be applied to obtain absolute rate constants for its reactions and energy transfer processes. However, relative rate constants can be obtained and are reported for CO2, Ar, and N2 relative to O2. These data are interpreted in light of the two published sets of values for the Einstein A factors, which differ by more than an order of magnitude. The need for accurate values of these A factors in order to convert our relative rate constants into absolute values, as well as to use in understanding the chemistry of the upper atmosphere, is discussed. The rotational temperature of OH is shown to be 308±18 °K in both excess H and excess O3.
Rotational excitation in the electron impact ionization of supercooled N2
Authors: DeKoven Benjamin M. , Levy Donald H. , Harris H. H. , Zegarski B. R. , Miller Terry A.
Published: February 2003

Electrons of controlled energy have been used to ionize and electronically excite N2 cooled to a translational temperature of <2 °K in a supersonic expansion either of pure N2 or 10% N2/Ar. This source likely provides N2 molecules ’’frozen out’’ in their N′′ = 0 and 1 rotational levels. The rotational state distribution of B 2Σ+uN+2 was determined by monitoring the rotationally resolved emission spectrum. Observation showed that even at high (∼500 eV) impact energies, the N+2 rotational distributions are inconsistent with selection rules (ΔN = ±1) for dipole excitation from N′′ = 0 and 1. For lower electron impact energies the angular momentum content of the excited N+2 ion increases sharply. These observations are rationalized by a model which invokes interactions between the ion and the ejected electron.
The effect of anisotropic higher order dispersive interactions on the conformational stabilities of argon clusters
Authors: Cooper Thomas M. , Birge Robert R.
Published: February 2003

The point–dipole interaction model of polarizability developed by Applequist is applied to a theory of long-range intermolecular dispersive forces to explore the effect of anisotropic many body interactions on the properties of various van der Waals complexes. Our anisotropic point–dipole interaction formalism appears to be significantly more accurate than isotropic pairwise formalisms at medium to large internuclear separations. At short internuclear distances, however, our procedures overestimate the dispersion energy due to the inherent neglect of electron exchange effects. Nevertheless, for large clusters of atoms or molecules, the present formalism provides a dependable and relatively rapid calculational approach to the analysis of many body dispersion forces. The only-time consuming calculation of the entire procedure is the inversion of a 3N×3N matrix, where N is the number of atoms in the van der Waals complex. Potential energy surfaces for three noble gas atoms are predicted to have minima for both the triangular and linear configurations. Isotropic pairwise calculations predict a minimum only for the triangular configuration. Three other types of clusters are also investigated: a linear array, a planar triangular lattice, and a hexagonal closest packed cluster. The typical effect of the anisotropic many body interactions is to lower the calculated dispersion energy by 5%–20%. The magnitude of the energy lowering is approximately proportional to the optical anisotropy of the system. Our results imply that anisotropic effects are only important when the optical anisotropy is larger than 0.001.
Laser studies of electronic excitation transfer in atomic calcium:  Ca(4s5p 1P1)+Ar⇄Ca(4s5p 3P2, 1, 0)+Ar
Authors: Pence William H. , Leone Stephen R.
Published: February 2003

Time-resolved nsec kinetic methods are used to measure state specific electronic excitation transfer for the near-resonant process: Ca(4s5p 1P1) +Ar ⇄k-1k1 Ca(4s5p 3P2,1,0)+Ar. In stimulated emission experiments it is found that the Ca(4s5p 3P2) level is preferentially populated. The rate constant k1 for the specific 3P2 channel is 5.2±0.5×10−11 cm3 molecule−1 sec−1. These results are discussed in terms of near-resonant spin changing collision mechanisms. Radiative lifetimes for Ca(4s5p 1P1) and Ca(4s5p 3P1) are also determined to be 77±2 nsec and 67±2 nsec, respectively.
Valence bond description of antiferromagnetic coupling in transition metal dimers
Authors: Noodleman Louis
Published: February 2003

A single configuration model containing nonorthogonal magnetic orbitals is developed to represent the important features of the antiferromagnetic state of a transition metal dimer. A state of mixed spin symmetry and lowered space symmetry is constructed which has both conceptual and practical computational value. Either unrestricted Hartree–Fock theory or spin polarized density functional theory, e.g., Xα theory, can be used to generate the mixed spin state wave function. The most important consequence of the theory is that the Heisenberg exchange coupling constant J can be calculated simply from the energies of the mixed spin state and the highest pure spin multiplet.
The spectroscopy of a benzil–bibenzyl mixed crystal system. Effects of isotopic substitution
Authors: Kohler Bryan E. , Loda Richard T.
Published: February 2003

We report the T = 4.2 K, S0→S1 excitation and T1→S0 emission spectra of five different isotopic derivatives of benzil doped into bibenzyl single crystals. Selective excitation of the individual components of the isotopic mixtures has been observed. The 0–0 transition energy shifts with isotopic substitutions are additive, as may be expected for systems where geometry changes upon excitation consist primarily of linear displacements of the normal coordinates.
The b component of the transition moment for the ν2 band of nitric acid vapor
Authors: Farrow L. A. , Richton R. E.
Published: February 2003

Transmittance data on dry nitric acid vapor at four CO laser frequencies are analyzed in conjunction with detailed spectral information on the ν2 band of HNO3. As a result, spectral line parameters have been obtained at each laser frequency, and the b component of the transition moment of the ν2 band has been determined to be (0.326±0.023) D.
The B
K method: Application to methylene
Authors: Davidson Ernest R. , McMurchie Larry E. , Day Sheryl J.
Published: February 2003

The BK method is compared with conventional CI and other perturbation methods for the 3B1 and 1A1 states of methylene. Use of Rayleigh–Schrödinger perturbation theory for construction of an effective Hamiltonian is seen to be more accurate for estimating the full CI energy limit.
Experimental studies of sodium-doped polyacetylene: Optical and ESR results for metallic (CHNay)x
Authors: Chung T-C. , Feldblum A. , Heeger A. J. , MacDiarmid A. G.
Published: February 2003

Optical absorption and ESR spectra of metallic Na-doped (CH)x are reported. The results indicate chemical n-type doping with no free sodium metal in the film. Analysis of the data leads to estimates of the conductivity (σ?3×103 Ω−1 cm−1) and susceptibility (χp?1.6×10−6 emu/mol). The results imply that the metallic state in doped (CH)x is very similar for both p- and n-type dopant species.
Picosecond infrared double resonance studies on SF6
Authors: Sharp Richard C. , Yablonovitch Eli , Bloembergen N.
Published: February 2003

A classic pump–probe experiment is performed on SF6. Using 30 psec pulses from two independently tunable CO2 lasers, we have studied the intramolecular energy transfer processes occurring in a collisionless environment. Distinct from nanosecond pulse experiments, we find an extremely narrow and deep hole burning feature at the pump wavelength. Experimental results exhibit both discrete state bottlenecking effects and quasicontinuum absorption. New evidence of an extremely rapid collisional relaxation is found, which may be related to rotational hole filling.
The two-center expansion of an exponential function: The reduction of Yasuda’s expression to that of Briels
Authors: Yasuda Hideo
Published: February 2003

It is shown that the two-center expansion for an exponential function derived by the author [J. Chem. Phys. 73, 3722 (1980)] is essentially identical with that of Briels [J. Chem. Phys. 73, 1850 (1980)] though different in approach. The simplification of our representation is also discussed.
Comment on the specific concentration dependence of the proton magnetic resonance chemical shift in the system acetic acid–water
Authors: Sims R. W. , Willcott M. R.
Published: February 2003

The anomaly in the chemical shifts of water and carboxyl group for acetic acid and water solutions is discussed. Kimtys and Balevicius’s results regarding the absence of such anomaly are disputed upon. The authors contend such an anomaly exists in the region of 20 wt.% water in acetic acid.(AIP)
A class of master equations that exhibit a generalized form of canonical invariance and other ‘‘displacement’’ invariances
Authors: Thiele Everett , Stone James , Goodman Myron F.
Published: February 2003

We introduce a definition for the displacement of two probability distributions, one with respect to the other, which generalizes mean value as a measure of displacement. This definition, like the definitions of mixing enhancement and mixing distance of Uhlmann and Ruch, provides a partial ordering scheme for probability vectors. We then show that for solutions to a physically interesting class of master equations the displacement property is preserved in time. By generalizing the definition of displacement to cover nth order time derivatives of the probability vector, we are able to prove a number of results concerning the nature of the approach to steady state. These results include useful sufficient conditions guaranteeing the monotonic approach to steady state value for various averages. On this basis, we suggest a more generally applicable version of the canonical invariance property found originally by Montroll and Shuler for the collisional relaxation of diatomics via Landau–Teller transition rates. Most of the derived results do not require the detailed balancing assumption appropriate to the relaxation of a system in contract with a heatbath, and thus apply to systems relaxing to a steady state that need not be at thermal equilibrium.
Theory of monolayer physical adsorption. II. Fluid phases on a periodic surface
Authors: Monson Peter A. , Steele William , Henderson Douglas
Published: February 2003

The submonolayer physical adsorption of a simple gas on an exposed single crystal face of an inert solid is treated. A perturbation theory is developed to treat the effect of periodic terms in the gas–solid energy. Monte Carlo computations of the properties of two-dimensional Lennard-Jones and hard-disc fluids are used as a reference system. Isotherms and heats of adsorption are evaluated for a number of values of the gas atom/surface lattice cell size ratio. It is shown that the inclusion of the periodicity has a considerable effect on these properties. In particular, the calculated adsorption isotherms suggest that there is an optimum adsorbate atom size for a given surface symmetry for which the two-dimensional critical temperature is maximized, in agreement with experimental observations.
Hydrogen in aromatics. I. Electrical conductivity and electron paramagnetic resonance of triphenylene–potassium complexes under hydrogen atmosphere
Authors: Enoki Toshiaki , Inokuchi Hiroo
Published: February 2003

Electrical conductivity and electron paramagnetic resonance are investigated for two kinds of triphenylene (Tp)–potassium complexes with different compositions TpK1.46 and TpK0.87 under hydrogen atmosphere. TpK1.46 shows a two-stage absorption process of hydrogen, consistent with the two-stage hydrogen–deuterium exchange reaction previously presented. At the first stage, we find the enhancements of the electrical conductivity and the spin concentration; these findings suggest that hydrogen molecules are dissociated into atoms in the complex crystal. We consider that the dissociated hydrogen atoms react with the complex to form hydride at the second stage, which causes a lowering of the conductivity and the spin concentration. In the case of TpK0.87, on the other hand, a one-stage absorption process is found. The introduction of hydrogen does not cause a large enhancement of the conductivity, while the spin concentration is lowered over the time course of the absorption; the absorbed hydrogen is regarded to react directly with the complex molecule to form hydride without the dissociated hydrogen state.
Activation energies and tunneling frequencies of ammonium halides and ammonium hexachlorides
Authors: Smith David
Published: February 2003

The activation energies for threefold and fourfold reorientations of the ammonium ion in cubic crystalline fields have been derived using the potential function v(ω) = βB[β3v3(ω)+β4v4(ω)+β6v6(ω)]. The improved zero-point energy correction of Svare et al. has been used. The activation energies computed for both the ordered and disordered bcc phases of the ammonium halides are somewhat lower than the observed values. The activation energies have also been computed for the ammonium hexachlorides. The parameters in the potential function for (NH4)2PbCl6, (NH4)2PtCl6, and (NH4)2PdCl6 have been determined from the librational frequencies. It is found that the β6v6 term in the potential function is very important for the analysis of the hindered rotation of the ammonium ion in these compounds.
A test of the accuracy of an effective pair potential for liquid water
Authors: Morse Michael D. , Rice Stuart A.
Published: February 2003

Water–water interactions are studied by examining the crystalline symmetries of the eight know forms of ice. (AIP)
Doppler-canceled, two-photon resonant ionization spectroscopy
Authors: Bushaw B. A. , Whitaker T. J.
Published: February 2003

The use of a pulse amplified cw dye laser is described in the first observation of hyperfine structure in the two-photon resonant, three-photon ionization spectrum of ground state Xe. (AIP).
The far-infrared spectrum of the tetragonal phase adamantane II at 4.6 °K
Authors: Bertie John E. , Francis Bernard F. , Jacobs Stephen M.
Published: February 2003

The far-infrared absorption spectrum of the tetragonal adamantane II contains the expected three bands, but with an unusual disparity between their intensities. Their frequencies agree well with those calculated by Luty, and coincide with three of the features in the published Raman spectrum which, however, contains at least 12 features instead of the expected five.
Nonadiabatic ionic–covalent transitions. Exponential–linear model for the process H++H−→H(2s,2p)+H(1s)
Authors: Borondo F. , Macías A. , Riera A.
Published: February 2003

Ion–ion recombination and asymmetrical charge transfer are two of a series of physical phenomena which are commonly explained through transitions taking place in the region where the energies of covalent and ionic states cross. To calculate the transition probability in this region, the Landau–Zener model is currently used, assuming that (i) ionic and covalent states are orthogonal in the crossing region; (ii) their radial coupling is negligible; (iii) the transition region is well localized. For the particular case of the states involved in the process H++H−→H(2s,2p)+H(1s), we show that none of these assumptions is fulfilled. As a conclusion, ab initio, asymptotic, and semiempirical methods which employ Landau–Zener theory to treat ion–covalent transitions should be tested with regards to the validity of the basic assumptions (i), (ii), and (iii); if necessary, an exponential–linear model should replace Landau–Zener theory.
Simple size-dependent combining rule for closed-shell repulsive interactions
Authors: Lee Hee Cheon , Kim Yung Sik
Published: February 2003

We present a simple method that incorporates the effect of the size differences of the constituent atoms or ions to the combining rules for the closed-shell repulsive interactions. The accuracy of the estimates of this method is compared with those of the other combining rules, such as the simple arithmetic and geometric mean rules and the Smith combining rule. Our estimates are usually better than the estimates of the other rules. For some cases, in which the other rules already give good results, ours are at least of the same accuracy.
Vibrational product states from reactions of CN− with the hydrogen halides and hydrogen atoms
Authors: Maricq M. Matti , Smith Mark A. , Simpson C. J. S. M. , Ellison G. Barney
Published: February 2003

Infrared chemiluminescence is observed from the C–H stretch manifold ν3 of HCN formed in the gas phase ion–molecule reactions: CN−+HX→HCN(v3)+X−, with (X = Cl, Br, I), and for CN−+H→HCN(v3)+e−. Qualitative information is also obtained for excitation in the bending mode. In each case some excitation is observed in the highest level allowed by energy conservation. Comparison with similar studies of the reactions Cl−+HX shows that the stretching mode of the newly formed bond is less efficiently populated in the HCN case. Emission is observed from CNH (hydroisocyanic acid) formed in the reaction CN−+HI→CNH(v)+I−.
Kinetic study of high-pressure Ar–H2O mixtures excited by relativistic electrons
Authors: Leblond J. B. , Collier F. , Hoffbeck F. , Cottin P.
Published: February 2003

Dissociation of the H2O molecule by collisions with metastable argon (3P2) was shown a few years ago to lead to the excitation of the first vibrational levels of A 2Σ+ excited state of OH. The present work consists of a detailed kinetic study of an e-beam excited Ar–H2O mixture to evaluate the potential interest of that reaction scheme for laser applications. In this study, we have mainly shown that OH* (A 2Σ+) is populated by an Ar++H2O pathway too and we give an estimate for the OH* (A 2Σ+) and OH (X 2Π) formation branching ratios. We have also estimated that Ar*2+H2O is a minor OH* pathway. These results and measurements of main reaction rates permitted us to give a kinetic model where the predicted time dependence of population are in good agreement with the experimental result. The feasibility of a radical laser based on the collisional dissociation scheme of molecules is discussed.
A theoretical study of unimolecular reactions of vinyl fluoride. Potential surface characteristics and their mechanistic implications
Authors: Kato Shigeki , Morokuma Keiji
Published: February 2003

A b inito MO calculations have been performed for potential energy surfaces of unimolecular reactions of vinyl fluoride. The geometries and energies of the reactant, transition states, reaction intermediates, and product have been determined for ten elementary reactions both on the triplet and the singlet surfaces. The mechanism of the unimolecular dissociation reaction has been discussed in terms of the energy diagram obtained by the present calculation and compared with the interpretation derived from photosensitizer and IR-multiphoton experiments. We have also calculated the intrinsic reaction coordinate (IRC) for the αα- and αβ-HF direct elimination reactions and discussed the mechanism of energy partitioning in the reaction product. We propose an experiment that would determine which of the αα and αβ processes is dominant in the HF elimination reaction.
Self-consistent, nonorthogonal group function approximation for polyatomic systems. II. Analysis of noncovalent interactions
Authors: Mehler Ernest L.
Published: February 2003

The self-consistent nonorthogonal group function (NOGF) approximation has been reformulated for the calculation and analysis of noncovalent interactions. With the help of perturbation theory it is shown that the present analysis differs from previous decompositions in the polarization interaction, and the source of this difference is exhibited. The method is applied to several H-bonded dimers and one non-H-bonded complex, and the results are compared with previous calculations. At the same time a complete basis set analysis is made for each system and corrected interaction energies and dipole moments are calculated. The relative reliability of the corrected and uncorrected quantities is discussed. The NOGF formalism is used to construct a wave function which accounts for a limited part of the charge transfer effect, and results are presented which show that for medium quality basis sets this wave function may be more reliable for the calculation of interaction properties of H-bonded complexes than the standard SCF–MO wave function.
Quantum chemistry by random walk: Importance sampling for H+3
Authors: Mentch Frank , Anderson James B.
Published: February 2003

The use of importance sampling with the random-walk method of solving the Schrödinger equation in a way devised by Ceperley is examined in its application to determining the electronic energy of ground state H+3. The improved method yields energies of higher accuracy than prior random-walk or variational calculations. The required computation effort remains large for high accuracy but might be reduced by improved trial wave functions used in importance sampling. For the equilateral triangle configuration with side length of 1.6500 a.u., the calculated total energy is −1.3439±0.0002 a.u. This value lies below the upper bound of −1.34335 a.u. established in the lowest-energy variational calculations by Salmon and Poshusta and above their estimate of −1.3447 a.u. as the true value. Energies calculated for four other nuclear configurations of interest in determining the vibrational frequencies of H+3 are found to be, typically, 0.001 to 0.003 a.u. lower than those of the most accurate variational calculations, but relative values of the energies are probably less accurate than those of the variational calculations.
Perturbation theory applied to potential energy surfaces. I. The choice of a suitable reference function ψ(0)
Authors: Nyden Marc R. , Petersson G. A.
Published: February 2003

The effect of the choice of zero order wave function on the accuracy of third-order perturbation theory is examined. The restricted Hartree–Fock, unrestricted Hartree–Fock, and generalized valence bond wave functions are considered as zero order wave functions for both Epstein–Nesbet and Mo/ller–Plesset perturbation theory. In each case the third-order perturbation results are reported for the H2 X1Σ+g potential energy curve. The behavior of Epstein–Nesbet perturbation theory relative to Mo/ller–Plesset perturbation theory is found to be independent of ψ(0). However, the nature of the perturbation and hence the absolute accuracy of both perturbation theories is determined by the choice of ψ(0). A comparison with CI calculations demonstrates that of the three examples, only the GVB perturbation theory is consistently accurate over the entire potential surface. The RHF expansion as expected becomes slowly convergent at large internuclear separations as a direct result of improper dissociation. On the other hand, the third-order UHF perturbation calculations have large errors (∼0.0225 hartree) at intermediate internuclear separations (3–4 bohr) where there is a strong contribution from single excitations. In contrast, the third-order EN–GVB perturbation theory has a maximum error of only 0.0001 hartree for any H2 geometry. The errors in the MP–GVB expansion for H2 are about an order of magnitude larger but can be considerably reduced (to ∼0.0002 hartree) by using the geometric approximation.
Effect of the local exchange-correlation correction to electron density on the properties of inorganic solids
Authors: Kucharczyk M. , Olszewski S.
Published: February 2003

In the density-functional theory one attempts to get the best possible functional for energy. Then the functional is used in the calculation of the properties of solids. In the present paper a very simple form for the functional is preserved but the density is corrected. The correction has negative sign and its main sense is to take into account the lowering of electron density due to the collective effect of the exchange and the correlation holes. The correction is postulated in the form of the Laplace operator acting on the exchange-correlation potential of the Wigner–Seitz–Slater type. The presence of the correction in the models based on the Thomas–Fermi–Dirac or Thomas–Fermi–Dirac–Gombás energy functionals makes it possible to get cohesion for monatomic solids of all elements in the periodic system; in the absence of the correction, the positive cohesive energy could not be obtained for any element in both models mentioned above. The volume dependence of the Grüneisen parameter for a number of metals has been calculated and a new derivation of the Dugdale–MacDonald formula is presented. It has been shown that the pressure of the electron gas on the ion boundary in an ionic crystal is adequate for an explanation of the repulsive forces between ions in the crystal. Values of the exponents of these forces, which usually are determined experimentally from the compressibility data, have been calculated theoretically. The ratios of the ab initio values of the ionic radii which are obtained from (a) the distances between the ionic nuclei and the boundaries of the ions, (b) the positions of the minima of electron density for ionic pairs, resemble respectively, the ratios of the semiempirical Pauling’s radii and the ratios of the similar radii obtained by Fumi and Tosi. On the basis of set (a) of the theoretical radii the structural properties of a number of binary compounds containing one metal ion and a number of ternary compounds containing several metal ions (perovskites, ilmenites, and spinels) have been examined. The predicted crystal structures are, in general, close to those observed in reality.
A new self-consistent-field valence bond method. I. Method for conjugated systems
Authors: Kuwajima Satoru
Published: February 2003

A new method of constructing orbital equations is presented. While this method can yield the Hartree–Fock equation, it is suited to treat wave functions constructed with nonorthogonal orbitals and produces tractable equations without relying on orthogonality restrictions. With the use of this method an SCF VB method is proposed for conjugated systems. This SCF VB method consists of an SCF equation and the usual procedure of the VB method of conjugated systems. The SCF equations is like the Hartree equation and it yields wholly nonorthogonal singly occupied orbitals. Test calculations are carried out on conjugated π systms (butadiene, hexatriene, and benzene) utilizing the Pariser–Parr–Pople model. The ground state energies considerably lower than the Hartree–Fock values are obtained with the use of only the covalent VB structures. Pure-covalent excited states, which are constructed with the same ortibals as the ground state, are also calculated and most of them turn out to be better than the corresponding single and double excitations CI results.
A ‘‘three-variable’’ theory of flow birefringence and its relation to V
H depolarized light scattering
Authors: Allen Michael P. , Chappell Philip J. , Kivelson Daniel
Published: February 2003

A three-variable theory of anisotropic relaxation, closely related to one previously described for VH depolarized light scattering, is described and applied to flow birefringence. The anisotropic dielectric fluctuations in liquids are described in terms of orientational and stress tensor (intermolecular) fluctuations. Even in liquids composed of symmetric top molecules, the intermolecular contributions to flow birefringence are predicted to be significant. Using the parameters obtained from light scattering, we calculate the stress-optical coefficient for triphenylphosphite over the temperature range 10–40 °C, and obtain approximate agreement with the values obtained from flow birefringence experiments. However, we find an appreciable discrepancy between the calculated and experimental temperature dependences.
On the lowest excited singlet state of osmium tetroxide
Authors: Swift K. M. , Bernstein E. R.
Published: February 2003

Two-photon spectra of OsO4 in the region below the first strong one-photon transition are observed and analyzed. The data fit a linear Jahn–Teller (T×t) calculation. An assignment of the two-photon features as arising from a T1 electronic state, origin at 27 295 cm−1, with a dominant linear Jahn–Teller active t2 vibration ν3, ν′3 = 588 cm−1 (ν′′3 = 960 cm−1), and with Jahn–Teller parameter D = 0.5 is proposed. Based on these findings the two observed one-photon states are discussed and qualitatively analyzed in a parallel fashion.
Photolytic codeposition generation of the HgF radical in an argon matrix at 12 K: An ESR investigation
Authors: Knight Lon B. , Fisher T. A. , Wise M. B.
Published: February 2003

The HgF radical has been generated by photolysis during the codeposition reaction of Hg atoms and F2(g) in an argon matrix at 12 K. The magnetic parameters are g(∥) = 1.993(1), g⊥ = 1.961(1); A∥ (19F) = 1344(10) MHz, A⊥ (19F) = 195(5), A∥ (199Hg) = 22 622(10), A⊥(199Hg) = 21 880(8), A∥ (201Hg) = 8055(12), A⊥ (201Hg) = 7760(10). Utilizing the g and A tensor data, the electronic structure of HgF is compared to the other MF radicals studied.
Electron spin resonance of Cr5+ in YPO4 and YVO4
Authors: Greenblatt M. , Pifer J. H. , McGarvey B. R. , Wanklyn B. M.
Published: February 2003

The ESR of CrO3−4 has been studied at 4.2 K in single crystal YPO4 and YVO4. The g values and 53Cr hyperfine constants are g∥ = 1.9772, g⊥ = 1.9525, A∥ = 8.5×10−4 cm−1, A⊥ = 19.6×10−4 cm−1 for YPO4 and g∥ = 1.9773, g⊥ = 1.9511, A∥ = 8.6×10−4 cm−1, A⊥ = 18.7×10−4 cm−1 for YVO4. The resonances show an isotropic superhyperfine splitting due to the two nearest neighbor yttrium ions. The PO4 and VO4 tetrahedra are distorted to D2d symmetry by a c axis stretch and a crystal field model predicts a dx2–y2 ground state for the d1 electron on CrO4 in these hosts. But a dz2 state is observed. We attribute the inversion to strong covalency. The g and A values cannot be explained with D2d symmetry and the width of the superhyperfine lines is orientation and magnetic field dependent. We believe these anomalies are due to motional effects.
Energy partitioning in the reaction 16O(1D)+H2 18O→16OH+18OH. II. The distribution of 16OH and 18OH
Authors: Gericke K.-H. , Comes F. J. , Levine R. D.
Published: February 2003

The reaction of O(1D) with water proceeding to two OH molecules has been studied by isotopic labeling of the oxygen atom in the water molecule in order to distinguish between the two chemically identical product molecules and to determine the product state distribution. A large fraction (∼0.6) of the available energy is released as translation. The vibrational energy is preferentially channeled into the new (16OH) bond, and the 16OH vibrational distribution is ’’hotter’’ than that expected on prior (microcanonical) grounds. The opposite is true for the 18OH (old bond), which is produced almost exclusively (≳0.9) in the ground vibrational state. The rotational energy is, however, equipartitioned among the two bonds. For each vibrational manifold, the rotational distribution is well characterized by a linear surprisal. Using a reduced variable, the rotational surprisal parameter is found to be independent of the vibrational state. Due to the high fraction of available energy released as translation, the fraction of energy in the rotation (∼0.2) is less than expected on prior grounds and the surprisal parameter is positive. The ratio of the rotational surprisal parameters determined for 16OH and 18OH by surprisal analysis is in close agreement with that predicted by the equipartitioning of the rotational energy between the two OH molecules. The OH was found to be statistically distributed between its two possible spin states.
Interpreting pulsed-gradient spin–echo diffusion experiments with permeable membranes
Authors: von Meerwall E. , Ferguson R. D.
Published: February 2003

We have developed an approximate expression for the spin–echo attenuation as function of the diffusion time in a pulsed-gradient experiment on specimens containing regularly spaced barriers of arbitrary permeability. The expression is a modification of the exact solution for impermeable barriers, and is simple enough to permit use in curve-fitting programs.
‘‘Spinodals’’ in the mean field theory of freezing
Authors: Klein W. , Brown Alan C.
Published: February 2003

We calculate, in the context of the mean field theory of freezing proposed by Grewe and Klein, exponents that characterize singularities at spinodal-like points. On the basis of the values of these exponents and the analogy of these ’’spinodal’’ points to critical points we predict an upper critical dimension dc = 6, above which these mean-field exponents are correct for realistic short range potentials. We also discuss the implication of these results for the Kirkwood instability analysis and bifurcation theories of the freezing transition.
Approximate formulas for Franck–Condon factors
Authors: Nicholls R. W.
Published: February 2003

Approximate formulas are derived which express small quantum number Franck–Condon factors as simple functions of a transition parameter u = μA?e(Δre)2/67.4425. These formulas give values which agree well with more elaborate calculations. They are particularly useful for band systems for which only rudimentary molecular data exist.
14N nuclear magnetic relaxation study of acetonitrile in carbon tetrachloride: An unexpected behavior at low concentration
Authors: Tiffon Bernard , Ancian Bernard , Dubois Jacques-Emile
Published: February 2003

An unexpected behavior at low concentration of the molecules liquid autonitrile in CCl4 is studied.(AIP)
The heat of formation of C2H+
Authors: Ono Y. , Ng C. Y.
Published: February 2003

The heat of formation of C2H+→C2H++H is considered.(AIP)
Comment on ‘‘An MCSCF characterization of the HeH2+ 2 2A1(2Σ+) polarization state. A radiative mechanism for the production of H+2 from thermal He++H2 collisions’’
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2003

The authors make their comment on the radiative mechanism for the production of H2 + from thermal He++H2 collisions.(AIP)
Reply to Johnsen and Biondi’s comment on ‘‘An MCSCF characterization of the HeH+2 2 2A1(2Σ+) polarization state. A radiative mechanism for the production of H+2 from thermal He++H2 collisions’’ [D. G. Hopper, J. Chem. Phys. 7
3, 3289 (1980)]
Authors: Hopper Darrel G.
Published: February 2003

The authors makes a discussion of the radiative mechanism for the production of H2+ from thermal He++H2 collisions.(AIP)
Electronic to vibrational rotational energy transfer in collisions of Na(3 2P) with NO and small organic molecules
Authors: Hertel I. V. , Reiland W.
Published: February 2003

The energy ΔEvibrot transferred by quenching Na(3 2P3/2) to internal degrees of freedom of NO and small organic molecules with double bonds (C2H4, C3H6, C4H6, C4H8, and C2H2) has been investigated in a crossed beam experiment with laser excited Na. The results for NO show a maximum cross section for small ΔEvibrot and are critically compared with findings of other groups. The energy transfer spectra of organic molecules show that between 40% and 80% of the available total energy is transferred to the molecule in the average. The results are analyzed in the framework of statistical prior distributions, which give good agreement with the experiment when we assume that only a small number of internal degrees of freedom participates in the reaction.
A realization of ‘‘V structure’’ in liquid water
Authors: Hirata Fumio , Rossky Peter J.
Published: February 2003

Results obtained from a molecular dynamics computer simulation of ST2 model water are used to generate a representation of liquid water which corresponds closely to the so-called ’’V structure’’ described by Eisenberg and Kauzmann. The representation is obtained by calculating a sequence of mean molecular positions, each mean being obtained by averaging the true dynamical center of mass and angular coordinates over a time comparable to the periods of hindered translational and rotational motion. For the averaging time used (τA = 0.2 psec), the results show significant narrowing in the distribution of nearest neighbor distances and of hydrogen bond angles. The distribution of molecular interaction energies manifests an associated shift to more negative values, and is somewhat narrower. Correspondingly, for a reasonable energetic criteria for an intact bond, the occurrence frequency of hydrogen bonds is dramatically increased in the V structure. The degree of connectivity of the hydrogen bond network shows parallel behavior. However, it is further shown that the energetic description of the V structure parallels that of the original, unmodified, structure, if corresponding intact hydrogen bond energy criteria are chosen reasonably. To obtain corresponding energetic structures, the criterion in the V structure must be shifted to more negative values to allow for the apparent loss there of a thermal excitation energyof about kBT. It is suggested that a time sequence of V structures can be a valuable source of information for the analysis of longer time scale dynamics, since the rapid and large amplitude librational motions are effectively averaged out. By the same token, a study of the temperature variation of the V structure should be able to separate the variation in structure arising from changes in the underlying hydrogen bond network from that due to changes in the thermal vibrational excitation of that network.
Computer simulations of a continuum system of molecules with a hard-core interaction in the grand canonical ensemble
Authors: Lee Young Seek , Chae Dong Ghie , Ree Taikyue , Ree Francis H.
Published: February 2003

A method to simulate a semi-infinite continuum system in the grand canonical ensemble is proposed. It uses a Monte Carlo method to evaluate the largest eignvalue of the Kramers–Wannier matrix. For a two-dimensional system of parallel hard squares the pressure and the density computed from the proposed grand-canonical-ensemble method show satisfactory agreement with the corresponding canonical-ensemble calculations at densities below 72% of the close-packed density. An approximate method for high-density calculations is proposed.
The field dependence of the Kirkwood factor and the nonlinear dielectric behavior of some liquids
Authors: Liszi J. , Mészáros L. , Ruff I.
Published: February 2003

An equation is deduced for the field dependence of relative permittivity of liquids making allowance for the field dependence of the Kirkwood g factor too. The equation gives predictions on both normal and anomalous dielectric saturation as well as on the structure-breaking or structure-making effect of the field. Comparison with experimental data indicates that the field dependence of the g factor can alter significantly the nonlinear coefficient Δε/E2 calculated for some alcohols, water, and nitrobenzene. Comparison is also made with approximations, published previously. It is indirectly confirmed that the dielectric behavior of liquids can be described by the same equation even in the vicinity of ions in electrolyte solutions, provided that the average field strength, calculated on the basis of the lattice model of electrolytes, does not exceed the value of about 104 esu. This is about 100 times stronger than the maximum field applied in macroscopic measurements of the nonlinear coefficient.
Monte Carlo studies of the structure of dilute aqueous sclutions of Li+, Na+, K+, F−, and Cl−
Authors: Mezei Mihaly , Beveridge David L.
Published: February 2003

Monte Carlo–Metropolis statistical thermodynamic computer simulations are reported for dilute aqueous solutions of Li+, Na+, K+, F−, and Cl−. The calculations are carried out on systems consisting of one ion and 215 water molecules at 25 °C and experimental densities. The condensed phase environment is modeled using periodic boundary conditions. The configurational energies are developed under the assumption of pairwise additivity by means of potential functions representative of nonempirical quantum mechanical calculations of the ion–water and water–water energies. The internal energies, radial distribution functions, and related thermodynamic properties are calculated for each system. The structure of the local solution environment around each dissolved ion is analyzed in terms of quasicomponent distribution functions. The results are compared with analogous calculations on a smaller system to estimate the effect of long-range forces in the ion–water potential function on the calculated results.
Electron thermalization in gases. III. Epithermal electron scavenging in rare gases
Authors: Mozumder A.
Published: February 2003

Earlier work on electron thermalization in rare gases by the author [J. Chem. Phys. 72, 1657 (1980); 72, 6289 (1980)] has been extended to include electron scavenging by an attaching compound present as a minor component. While the cooling rate for the surviving fraction proceeds as in the pure gas, the scavenging rate is calculated using a time-dependent velocity distribution function and a velocity-dependent attachment cross section. For the last mentioned item, functions decreasing with a certain power of velocity specific to a given scavenger have been experimentally found by Christophorou and co-workers; the same are used with analytical extension. In general, epithermal scavenging has been found to be ubiquitous and time dependent. It depends mainly on the thermalization time, relative scavenger concentration, temperature, and thermal attachment cross section. Relative scavenger effectiveness has been found to be temperature dependent. In a simple case autodetachment has been included in the calculation using SF6 as an example. Both attachment and detachment compete with thermalization, the equilibrium being established only in the postthermal regime. To ensure purely thermal reactions in a rare gas such as Ar, which has the longest thermalization time of all the rare gases, purification from reactive scavengers must be carried to the level of 1 ppb (part per billion) or better. For other rare gases the requirement may be less stringent.