bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of thermophysical properties of a large polar molecule and application to homogeneous nucleation of l-menthol
Authors: Becker Carol , Reiss Howard , Heist Richard H.
Published: February 2003

The classical Becker–Doering theory has predicted to within 5% the critical supersaturations required for homogeneous nucleation for more than a dozen molecules. These successes have prompted us to investigate whether the classical theory can predict the experimental results for more extreme cases, i.e., high temperature measurements on large, polar molecules with hydrogen-bonding functional groups, like l-menthol. It is therefore the purpose of this paper (1) to report high temperature diffusion cloud chamber measurements on 1-menthol vapor; (2) to present the thermophysical properties, data or calculated values, required for (a) the experiment, i.e., the mass and heat flux equations, (b) the theory, and (c) the film correction; and (3) to compare the predictions of the Becker–Doering theory with the experimental results. Critical supersaturations, measured over the temperature range 41–100 °C, are about 7% higher than those predicted by the theory. Applying a film correction to the raw data brings the experimental envelope to within 5% of the theoretical curve. On the basis of this success the classical theory can indeed be extended to include high temperatures and unique molecules. However, the experimental results lie above the theory curve, indicating that menthol may be somewhat associated in the vapor phase. Accurate experimental supersaturations can be obtained for a molecule even though its thermophysical properties are scarce. Except for the vapor pressure, all the properties of menthol used in the mass and heat flux equations are calculated by reliable theoretical or empirical estimation methods. Varying each property by an amount equal to the error inherent in the corresponding estimation method has an insignificant effect on the supersaturation profile in the chamber. In fact, neglecting the film correction is a larger source of experimental error than estimating all the properties (except the vapor pressure) required to solve the mass abd heat flux equations. Since the vapor pressure is critical to the experimental results, one set of self-consistent vapor pressure data for menthol, measured over the range 30–175 °C, is needed. Given a more accurate vapor pressure expression, we can determine to what degree menthol is associated in the vapor.
Continuum states for hydrogen molecule: A study of convergence in e−–H2+ scattering equations
Authors: Tambe B. R. , Ritchie Burke
Published: February 2003

We study the scattering of electrons from singly ionized molecular hydrogen in order to obtain converged wavefunctions for the continuum states of molecular hydrogen. In view of the sensitivity of photoionization process to the details of the continuum wavefunction, we have investigated the accuracy of the various approximations that are used to deal with all the principal interactions. This has been done through the solution of a set of coupled integrodifferential equations which result from the analysis of e−–H2+ scattering in the close-coupling approximation. Finally, we give converged phase shifts for the continuum state wavefunction.
Bands associated with Cs(6 2S1/2) – Cs(7 2S1/2 and 5 2D5/2) transitions perturbed by helium
Authors: Sayer B. , Ferray M. , Visticot J. P. , Lozingot J.
Published: February 2003

New bands are observed in the absorption and emission spectra of a cesium helium mixture by using a laser induced fluorescence technique. The comparison between these spectra and those already obtained with the other cesium–rare gas systems allows us to associate these bands with transitions between the ground state and the 7 2S1/2 and 5 2D5/2 excited states of cesium perturbed by helium atoms. The analysis of the bands profile gives information about the shape of the adiabatic potential energy curves.
Towards a molecular theory of freezing: The equation of state and free energy from the first BBGKY equation
Authors: Raveché Harold J. , Kayser Richard F.
Published: February 2003

We determine crystalline solutions of a closed BBGKY equation for the local density in a classical hard sphere system. The inhomogeneous solutions, which bifurcate from the fluid phase, are applied to calculate the equation of state and free energy. A first order phase change is found in two and three dimensions and its existence is shown to depend on the direction of bifurcation and on global properties of the solutions. The results are discussed in terms of the closure.
Surface tension calculations for molten salts: Critique and modification of the Fowler model
Authors: Pastor R. W. , Goodisman J.
Published: February 2003

The Fowler model, the ubiquitous first approximation for calculations of surface properties, allows the calculation of surface tension and surface energy in terms of properties of the bulk fluid. It is here applied to a two-component fluid with Coulombic forces (molten salts), the bulk fluid being described by the generalized mean spherical approximation. In sharp contrast to universal experience with simple fluids, totally unreasonable results are attained. The situation is not improved by going to a more realistic model of the bulk fluid or by modifying the one-particle part of the pair distribution function. Inconsistencies in the Fowler model are discussed. Concluding that the difficulty lies in the violation of the electroneutrality condition demanded by the Coulombic forces, we give a simple method to guarantee its fulfillment. While hardly complicating the calculation, it gives drastic improvement in both surface tension and surface energy.
Subspace quantum mechanics and the variational principle
Authors: Srebrenik Shalom , Bader Richard F. W. , Nguyen-Dang T. Tung
Published: February 2003

This work is a continuation and extension of the delineation of the properties of a quantum subspace—a region of the real space of a molecular system bounded by a surface through which the flux in the gradient of the (observable) charge density is zero. Such subspaces are of interest as they constitute a basis for theoretical definitions of chemical concepts as obtained through experiment. The subspace stationary state variational principle, which was previously used to define this particular class of subspaces, reveals a close interrelationship between the hypervirial theorem and the variational property of the energy. By exploiting this interrelationship, one may obtain a variational solution to Schrödinger’s equation with the zero-flux surface requirement serving as a variational constraint. The connection between the statement of the subspace variational principle and the result of perturbation theory is established at the level of the first-order correction to the total energy. The statement of the generalized time-dependent subspace variational principle is derived using a modified form of Hamilton’s principle. The principle is also a variational statement of a time-dependent hypervirial theorem, generalized to systems bounded by surfaces of zero-flux in the gradient of the charge density. It, therefore, enables one to describe the time dependence of subspace averaged properties. The use of virial sharing operators, which permit the definition of single particle potential energies, in a quantum analogue of Hamilton’s extended principle, leads to a unique variational definition of the electronic energy within the Born–Oppenheimer approximation. In terms of this extended principle, both the classical and the quantum equations of motion are obtained for systems in which forces of constraint are operative by demanding that the integral of the variation of the kinetic energy plus the virtual work involved in the variation be zero. As a result of this discussion, the total energy of a subspace of a molecular system is defined in terms of separate electronic and nuclear contributions. This definition of the energy of a subspace applies whether or not applied forces are acting on the nuclei of the system.
Cl-LII,III fluorescent x-ray spectra measurement and analysis for the molecular orbital structure of ClO4−, ClO3−, and ClO2−
Authors: Henke Burton L. , Perera Rupert C. C. , Urch David S.
Published: February 2003

The chlorine LII, III low energy x-ray spectra from sodium perchlorate, chlorate and chlorite have been obtained using carbon Kα (277 eV) photon excitation and a lead myristate analyzing ’’crystal’’ (2d=80 A). X-ray induced decomposition was observed for each of these compounds. By taking repeated spectral scans, systematically distributed over six samples, it was possible to extrapolate to ’’zero-dose’’ Cl-LII, III spectra. A specially developed least-squares fitting program was applied to precisely determine the energy and strength of each spectral component which utilized the known collimation and crystal broadening functions and yielded energy resolutions of less than 1 eV. Broad low-energy satellite structures were observed for all the oxy-anions and for chloride (NaCl) and have been compared to similar satellites as measured in the Ar-LII, III spectrum. These structures were thus identified as resulting from multielectron processes. The other peaks in the Cl-LII, III spectra of the oxy-anions could be understood as corresponding to transitions from molecular orbitals with Cl 3s or 3d character. These results have demonstrated that 3d orbitals do play a definite role in the formation of chemical bonds in the oxy-anions of chlorine and that the importance of this role increases with the oxidation state of the chlorine. Satisfactory correlations have been obtained with the complementary Kβ x-ray emission and photoelectron spectra and with molecular orbital theory for the same anions.
The interfacial density profile of a Lennard-Jones fluid in contact with a (100) Lennard-Jones wall and its relationship to idealized fluid/wall systems: A Monte Carlo simulation
Authors: Abraham Farid F.
Published: February 2003

Using the Monte Carlo simulation method, we study the interfacial liquid density profile for several systems; Lennard-Jones (L-J) fluid/L-J (100) solid fcc face, L-J fluid/L-J (10–4) wall, L-J fluid/’’Boltzmann averaged’’ wall, L-J fluid/hard wall, and hard-sphere fluid/Boltzmann averaged wall. Upon comparing the simulation results, we conclude that the Boltzmann averaged wall is a good effective one-dimensional potential for a (100) structured wall, and that the attractive interactions between the fluid atoms significantly influence the interfacial fluid density profile.
Photoselection with intense laser pulses
Authors: Magde Douglas
Published: February 2003

The method of photoselection uses a polarized photon beam to create a preferentially oriented population of excited state molecules. This population is examined using polarized absorption or emission techniques in order to obtain information about the symmetries of transition moments. Prelaser photoselection was limited in application to exceptionally long-lived states (or stable photoproducts) in perfectly rigid matrices or to strongly fluorescent states in moderately viscous media. With lasers, extension is possible to almost any state with a lifetime of picoseconds or longer, making photoselection a very powerful, general technique. This paper rederives the expected experimental behavior and extends the calculations to include saturation effects, which are prominent in practical laser experiments but were not important in classical studies. Furthermore, it shows that in the nonlinear regime, information on transition moment symmetry is available even from a single beam experiment. One very simple experiment is reported which verifies that one can distinguish ’’planar’’ from ’’linear’’ symmetry in absorbers using absorption methods in very fluid media. These results are most timely for picosecond mode-locked laser experiments but apply also to nanosecond Q switched or even intense continuous wave laser studies.
Molecular asymmetry: A correlation between the anisotropy parameter of the polarizability and the shape of the electron–density contour diagram
Authors: Winicur Daniel H.
Published: February 2003

An empirical relation is presented between the anisotropy parameter κ of the polarizability of diatomic molecules and a feature characterizing the shape of the 0.002 a.u. electron density contour, calculated to the Hartree–Fock limit. This correlation provides a means of estimating κ to within about 6% for a wide variety of diatomic types and also predicts the existence of negative values of κ.
Intermolecular potentials by the inversion of differential cross sections. V. ArKr
Authors: Buck U. , Huisken F. , Pauly H. , Schleusener J.
Published: February 2003

The differential cross section for ArKr is measured at the energy of E=64.9 meV. Rainbow and fast oscillations are well resolved. The data are directly inverted to the potential by the procedure described in Paper I [J. Chem. Phys. 54, 1923 (1971)] of this series. The potential with the minimum parameters ε=14.4 meV and Rm=3.88 Å is able to reproduce both the measured integral cross section and the second virial coefficient in an excellent manner.
Energy transfer in atom–diatom collisions: Vibronic excitation
Authors: Kelley J. D. , Bearman G. H. , Harris H. H. , Leventhal J. J.
Published: February 2003

Product state distributions from charge-transfer collisions between Ar+–N2 and H+–O2 as well as collision-induced excitation involving N+2 on He, Ar, and Xe are presented. These data, obtained from collision-produced emission spectra, are compared with a Franck–Condon model for the excitation-radiation process; significant deviations are observed and explained on the basis of a qualitative curve-crossing model formulated to treat such vibronic excitation processes.
Electronic to vibrational energy transfer from I (5 2P1/2). I. HCl, HBr, and NO
Authors: Grimley A. J. , Houston P. L.
Published: February 2003

Deactivation of I* (2P1/2) by HCl, HBr, and NO is directly observed to produce vibrationally excited states of the diatoms. The total deactivation rates are determined from either the decay of I* fluorescence or the rise of diatom fluorescence to be kEHCl= (4.46±0.77) ×102, kEHBr= (3.51±0.12) ×103, and kENO= (3.88±0.32) ×103 sec−1 torr−1. By comparing the intensity of I* fluorescence to that of the diatom it is found that the average number of vibrational quanta excited per deactivation of I* is 1.7±0.5, 2.3±0.5, and 3.4±0.7 for HCl, HBr, and NO, respectively. These findings are discussed in terms of recent models for E→V transfer.
Depolarized Rayleigh scattering from benzonitrile
Authors: Alms G. R. , Patterson G. D.
Published: February 2003

The depolarized Rayleigh light scattering spectrum of benzonitrile has been studied from −10 to 20°C and a corresponding range of 0.070–0.019 for q2η/ρΓ. Over this temperature range the central Rayleigh dip is clearly resolved, and the value of the rotational–translational coupling parameter R is determined. For benzonitrile, R=0.36±0.03, and is constant over this temperature range. This result is similar to that of all other liquids studied thus far. The temperature dependence of the depolarized linewidth is also studied and the pair molecular relaxation time determined. It is found that the slip model of rotational diffusion agrees with the pair molecular relaxation time when the static pair correlations are taken into account.
Vibrational transitions in N2–O2 collisions: A theoretical treatment and comparison with computer calculations
Authors: Jolicard Georges
Published: February 2003

Vibration–translation and vibration–vibration–translation energy transfers during an N2–O2 collisions are studied using a semiclassical treatment. The comparison with recent computer calculations confirms the validity of our approach and enables us to judge the effect of the simultaneous influence of different perturbations. Translational distorsion appears to have a considerable influence.
Improved calculation of nonlinear electric susceptibilities of conjugated hydrocarbon chains
Authors: McIntyre Eugene F. , Hameka Hendrik F.
Published: February 2003

We calculated the three relevant tensor components of the third-order electric susceptibilities of conjugated hydrocarbon chains in order to determine the space fixed third-order electric susceptibilities χxxxx–. We found that the space fixed susceptibility χxxxx differs significantly from the molecular parameter χXXXX.
High spin molecules: ESR of MnF and MnF2 at 4°K
Authors: DeVore T. C. , Van Zee R. J. , Weltner W.
Published: February 2003

ESR spectra of the MnF and MnF2 molecules trapped in neon and argon matrices have been observed at 4°K. MnF was found to have a 7Σ ground state with the following magnetic parameters in solid neon (assuming g∥=2.002): g⊥=1.999(1), ‖D‖=−0.0107(1) cm−1, ‖A∥(Mn) ‖=490(5), ‖A⊥(Mn) ‖=418(1), ‖A⊥(F) ‖=60(1), and ‖A∥(F) ‖=85(2) MHz. MnF is then highly ionic with the spin density on each F− probably less than about 5%. The Mn+ ion exhibits about 60% of the s character of the free ion. MnF2 is linear with a 6Σg ground state with magnetic parameters in solid neon (assuming g∥=2.002): g⊥=1.994(5), ‖D‖=0.370(3) cm−1, ‖A∥(Mn) ‖=153(6), ‖A⊥(Mn) ‖=124(1), ‖A⊥(F) ‖=19(1) MHz. Comparison of these parameters is made with those obtained earlier from crystalline MnF2 and similar magnetic crystals.
Translational energies from triatomic negative ions fragmentation
Authors: Goursaud S. , Sizun M. , Fiquet-Fayard F.
Published: February 2003

The dissociation of triatomic negative ions is studied with a classical trajectory method. The initial conditions are represented by the Wigner probability density function; the Hamilton equations of the motion are solved using the Bulirsch–Stoer algorithm and the final averaged values are obtained through a Monte Carlo sampling method. The use of different molecular models allows an evaluation of the assumptions made in the former simpler model. An analytical semi-empirical potential energy surface is built to represent an attractive negative ion state. The kinetic energy distributions calculated using such surfaces exhibit a maximum close to zero, opposite to what has been obtained with LEPS repulsive surfaces. The kinetic energy distributions appear to be relatively insensitive to the value of the autodetachment rate and to the shape of the surface. The main feature of the VFM surfaces is to introduce a strong translation to vibration coupling. Furthermore, the partitioning of the excess energy of the dissociation between translational and internal energies of the recoiling fragments, which favors the internal energy, is found to be independent of the amount of energy to be partitioned.
Rotational friction coefficients of a bumpy cylinder with slipping and sticking boundary conditions
Authors: Zwanzig Robert
Published: February 2003

Exact expressions are reported for the rotational friction coefficients of an infinite cylinder with a curtate hypocycloid cross section, for both slipping and sticking boundary conditions. Surface roughness on a molecular scale justifies use of the sticking boundary condition when the cylinder radius is larger than 500–1000 Å.
Excited hydrogen and argon atom production by charge transfer of metastable Ar+ ions in H2 molecules
Authors: Rothwell H. L. , Amme R. C. , Van Zyl B.
Published: February 2003

Observations of excited products from charge-transfering collisional between Ar ions and molecular hydrogen are reported.(AIP)
Concerning the existence of H− ion in irradiated solvent matrices at 77 K studied by stimulated luminescence
Authors: Truong T. B.
Published: February 2003

The attribution of the ∼1050 nm stimulation luminescence (SL) band in γ-irradiated pure solvent matrices at 77 K to the anion H− is further supported by the present SL results observed on irradiated neutral or acidic solid solutions of tetramethyl-p-phenylenediamine (TMPD), tryptophan, or diphenyl-p-phenylenediamine (DPPD) in methylcyclohexane (MCH), 4.5M CaCl2 ices and 2-methyltetrahydrofuran (MTHF). Depending on the location of its SL band, at the red side or the blue side of the e−s one, the anion H− can decay faster or slower, respectively, relative to the e−s in the irradiated matrix. The present two photon bleaching SL experiments in the region below the SL energy threshold support the suggestion that the e−s optical absorption band in γ-irradiated MTHF consists of many underlying discrete bands. There are three strongly overlapping bands : 1050, 1200, and 1400 nm. One of these, the 1050 nm, would be related to the anion H−. The effect of the γ-dose rate on the SL intensity in irradiated TMPD–MCH and DPPD–MTHF glasses at 77 K reveals that (a) for the same total γ-dose the formation of solvent radical is more pronounced in samples with higher γ-dose rate; (b) the solvent radical anion(s) might have an optical absorption band located in the same region as the e−s one.
The incomplete basis set problem. I. Perturbative corrections to Hartree–Fock energies
Authors: McDowell Keith
Published: February 2003

A perturbation procedure employing reduced free-particle Green’s functions is developed which yields systematic corrections to the incomplete-basis-set Hartree–Fock energy. Calculations for helium show that the corrections tend to converge to the exact Hartree–Fock limit.
Relaxation of the first excited 1u state of Hg2
Authors: Stock M. , Smith E. W. , Drullinger R. E. , Hessel M. M.
Published: February 2003

The decay of the 335 nm Hg2 fluorescence band was measured with 1 nsec time resolution for the first 200 nsec following optical excitation by a 10 nsec laser pulse. Measurements of the decay rates for various wavelengths in this band were used to analyze the relaxation of the vibrational levels in the 1u state. It was found that the lower vibrational levels quickly reach a Boltzmann distribution described by an effective temperature Teff. This effective temperature then decreases with time, asymptotically approaching the gas temperature. Comparison of these data with a model calculation by Montroll and Shuler yields a transition rate of 5.2×10−11 cm3 sec−1 for the transition between the two lowest vibrational states. Analysis of the relaxation for higher vibrational levels gave a value of 2.7×10−10 cm3 sec−1 for the 1u→0−g transition rate. Since no mercury trimers have been formed at these early times, the 485 nm fluorescence band is not present. It was therefore possible to evaluate the repulsive wall of the 1u potential curve for small internuclear distances corresponding to wavelengths in the red wing of the 335 nm dimer band which are normally overlapped by the 485 nm trimer band.
Pressure dependence in the multiphoton dissociation of 32SF6
Authors: Bado P. , van den Bergh H.
Published: February 2003

The multiphoton dissociation of 32SF6 has been studied in the presence of several inert gases. The reciprocal dissociation yields increase with increasing total pressure in a nonlinear way for the conditions applied. Different collisional quenching efficiencies are obtained for the various inert gases. From the quenching efficiencies information on the optical pumping process may be obtained.
Role of the Sternheimer effect in the ligand field splitting of nuclear and electronic levels
Authors: Gupta R. P. , Tse J. S. , Bancroft G. M.
Published: February 2003

We show that the polarization of atomic orbitals in molecules can be adequately taken into account by Sternheimer shielding–antishielding parameters calculated for appropriate sites. Covalent as well as ionic molecules can be treated by this simple approach to obtain agreement between ligand fields responsible for the splitting of electronic energy levels observed by photoelectron spectroscopy and for the experimentally measured nuclear quadrupole coupling constants.
Polyhalide photofragment spectra. II. Ultraviolet photodissociation dynamics of UF6
Authors: Kroger Peter M. , Riley Stephen J. , Kwei George H.
Published: February 2003

Phtotfragment spectroscopy of UF6 at a wavelength of 266 nm shows evidence for direct photodissociation to F atoms and UF5 radicals. A bimodal distribution of F-atom flight times and nonisotropic recoil angular distributions are found. UF5 fragments are formed with two distinct internal energy distributions separated by approximately 10 kcal mole−1. Measurements of photofragment production as a function of photolyzing light intensity rule out the possibility of a sequential two photon process. Analysis in terms of the UF6 absorption spectrum suggests both UF5 internal energy distributions involve UF5 radicals that are electronically excited with different amounts of electronic and vibrational energy. Population of these two distributions could arise either from absorption to two different electronically excited states of UF6 or from a single excited state that undergoes a curve crossing in the exit channel. The nonisotropic photofragment angular distributions imply both internal energy distributions evolve from UF6 states that are not octahedral in configuration. The nature of this geometrical distortion and its relationship to vibronic transitions in UF6 are discussed.
Statistical mechanics of small chain molecules in liquids. I. Effects of liquid packing on conformational structures
Authors: Pratt Lawrence R. , Hsu C. S. , Chandler David
Published: February 2003

When a chain molecule can be viewed as a collection of overlapping spherical groups, the effect of a solvent on the conformational structure of the chain molecule is described by the distribution function for the cavity particles associated with the spherical groups. This article discusses the calculation of the cavity distribution function for n-butane disolved in various apolar solvents: the liquids carbon tetrachloride, n-butane, and n-hexane. We consider the common picture where the CH3 and CH2 groups in n-butane are simple spheres. For that model, the cavity distribution function is a four-point correlation function. We find that the superposition approximation for the four-point function, while qualitatively correct, overestimates the effects of the solvent. An alternative scheme, which is called the two cavity model, yields results that agree quantitatively with a computer simulation study of liquid n-butane. We find that a solvent medium produces significant shifts in the conformational equilibrium of n-butane from that found in the gas phase. This phenomenon is the result of the nature of the local packing of solvent molecules neighboring the solute species under investigation. The conformational equilibrium is sensitive to this packing. The bulk packing fractions (molecular density times the volume of the molecule) of the liquids CCl4 and C4H10 are nearly identical. Even so there are noticeable differences between the intramolecular structure of n-butane in liquid carbon tetrachloride and in the neat liquid. Previous ideas on conformational equilibria have ignored the importance of steric (i.e., liquid packing) effects, and have assumed that solvent shifts in conformational structures can be attributed entirely to dielectric effects. Our calculations show that this assumption is wrong. The n-butane molecule contains no significantly polar groups. yet solvent media produce substantial shifts. For example, the trans–gauche equilibrium constant, xg/xt, for n-butane in the gas phase at room temperature is roughly 0.5, while we find it is about 1.0 when n-butane is dissolved in liquid CCl4 at the same temperature and 1 atm pressure. We discuss why the phenomenon has been overlooked, and suggest experiments to document its existence.
Statistical mechanics of small chain molecules in liquids. II. Intermolecular pair correlations for liquid n-butane
Authors: Hsu C. S. , Pratt Lawrence R. , Chandler David
Published: February 2003

In this article the intermolecular structure of liquid n-butane is studied with an application of the RISM integral equation. It is found that the pair correlations between atoms in different n-butane molecules do depend upon the nature of the intramolecular trans–gauche conformational equilibrium. An incorrect picture of the liquid structure is obtained if it is assumed that the fluid is composed only of trans conformers—the species most favored energetically. The local packing of CH3 and CH2 groups in the liquid is discussed. Particular attention is focused on the prediction of the Chandler–Pratt theory, which says that steric effects produce a solvent shift in conformational equilibria in liquid n-butane. It is shown that x-ray diffraction experiments can provide a direct probe of this phenomenon.
Deflagration and extinction of fuel droplet in a weakly-reactive atmosphere
Authors: Law C. K.
Published: February 2003

The combustion of a fuel droplet in an oxidizing environment consisting of a small quantity of its own vapor is analyzed, in the limit of large activation energy, using matched asymptotic technique. The zeroth-order solution yields explicit expresssions for the steady deflagration characteristics indicating that with increasing ambient fuel vapor concentration the flame size and temperature both increase whereas the droplet surface regression rate remains unchanged. The first order expansion yields the flame structure and a set of numerically-obtained universal curves representing the extinction limits of the system.
Electronic Green’s function for a linear crystal in a thermal gradient
Authors: Greer William L. , Haus J. W.
Published: February 2003

By employing a modification to Lloyd’s exactly solvable model [P. Lloyd, J. Phys. C 2, 1717 (1969)], we have evaluated exactly the configuration-averaged Green’s function for an electron (or exciton) in a one-dimensional crystal subjected to a thermal gradient. Our formalism is applied both to a continuous lattice in which the otherwise free electron experiences a randomly fluctuating potential at all points in the crystal, and to the discrete lattice in which the thermal fluctuations are confined to specified sites. The thermal gradient is incorporated by requiring that the root mean square potential fluctuation varies linearly with position. We compare the spectral density A (k,ω) so obtained with that appropriate to thermal equilibrium. Comments on transport properties are also included.
The lattice dynamics of the deuterium peroxide crystal
Authors: Trevino S. F. , Farr M. K. , Giguére P. A. , Arnau J. L.
Published: February 2003

The phonons propagating along the unique fourfold axis in the D2O2 crystal have been measured by coherent inelastic neutron scattering. The measurements covered all branches below 250 cm−1 (31 meV), which include all the motions of the rigid molecule, except rotation about the minor axis (close to the O–O axis of the molecule). The sample consisted of a single crystal of 99% isotopically pure D2O2 in the form of a cylinder 1.5 cm diam and 4 cm long. Group-theoretical selection rules for the observation of the phonons were calculated and used extensively as an aid in the classification and measurement of the phonons. Agreement with previously observed Γ point modes in infrared absorption and Raman scattering was fairly good, but necessitated reassignment of one E mode. A covalent force model, developed in an attempt to reproduce the observations, was only partly successful. The model served to describe the character of the phonon as librational or translational. It is reasonably consistent with the observed intensities of the phonons. The limit success of the model indicates the need for longer range forces than those described as stretching and bending of hydrogen bonds.
Theory of magnetic linearly polarized emission. I. Paramagnetic molecules in a rigid isotropic medium
Authors: Riehl J. P. , Richardson F. S.
Published: February 2003

A formal theoretical treatment of magnetic linearly polarized emission (MLPE) is developed for luminescent molecular systems. In the MLPE experiment, a constant magnetic field is applied to a luminescent sample and the emission is detected along a direction orthogonal to the direction of the applied field. The emission is analyzed for its linear polarization parallel (∥) and perpendicular (⊥) to the direction of the applied magnetic field, and the principal MLPE observable is ΔI=I∥−I⊥ (where I denotes emission intensity). Excitation may be accomplished along any direction and it may be polarized or unpolarized. Explicit theoretical consideration is given to the MLPE spectra of molecular systems possessing either a paramagnetic emitting state or a paramagnetic ground state. The influence of excitation photoselection processes, excitation–emission experimental geometries, magnetic field strengths, and temperature on the MLPE spectra of such systems is examined for the case in which the molecules are embedded in a rigid, isotropic medium (such as a solid matrix or glass). MLPE spectra are calculated for a number of model systems as a function of various experimental and molecular parameters. Relationships between MLPE observables and molecular spectroscopic and structural properties are discussed.
The structure of the ethyl radical
Authors: Pacansky J. , Dupuis M.
Published: February 2003

A consistent experimental and theoretical view is presented for the structure of the ethyl radical. These results show that the stable conformation is the staggered form and that the CH3 group in the radical is distorted.
The absorption spectra and excited state relaxation properties of lanthanide and actinide halide vapor complexes. I. ErCl3(AlCl3)x
Authors: Carnall W. T. , Hessler Jan P. , Hoekstra H. R. , Williams C. W.
Published: February 2003

The absorption spectrum of the vapor complex formed at elevated temperatures between ErCl3 and AlCl3 has been measured in the region 6000–44000 cm−1. The absorption band intensities were analyzed using the Judd–Ofelt theory for electric–dipole transitions. A good correlation between theory and experiment was obtained with the intensity parameters Ω2=25.8, Ω4=2.70, Ω6=2.01, all ×10−20 cm2. Based on this analysis, the radiative lifetimes of several excited states were computed, and the principal paths for radiative relaxation of these states were determined. The relationship between the existence of intense hypersensitive bands in the spectrum of the vapor complex and the site symmetry of the Er atoms is discussed, as is the possible use of Rydberg and charge transfer states for optically pumping the fn-states.
Microwave spectrum, dipole moment, and the conformation of 7-oxabicyclo[4.1.0]hept-3-ene
Authors: Chao S. , Cook Robert L. , Malloy Thomas B.
Published: February 2003

The microwave spectrum of 7-oxabicyclo[4.1.0]hept-3-ene has been studied and the rotational constants for the ground state are (in MHz) A=4073.15±0.01, B=3394.54±0.01, C=2174.07±0.01. Stark effect measurements have allowed determination of the dipole moment components μa=0.775±0.002 D and μc=1.770±0.005 D for a total dipole moment μ=1.932±0.005 D. Analysis of these data indicates the molecule has a boat conformation.
Vibrational excitation of N2 during optical pumping of Hg by 253.7 mμ resonance radiation
Authors: Degani J. , Rosenfeld E. , Yatsiv S.
Published: February 2003

The observed decay time and the population density of the metastable 6 3P0 state of mercury in a N2:Hg gas mixture are markedly reduced with increased duration of an intense 253.7 mμ resonance radiation pulse. We show that this phenomenon is due to a vibrational excitation of the nitrogen in the spin–orbit relaxation decay of the 6 3P1 to the 3P0 state of Hg which is followed by the quenching of the 3P0 state. Such quenching takes place by diffusion and deactivation of 3P0 at the walls or by a three-body excimer formation in the gas. Observations are confirmed by a numerical solution of the rate equations for the different excited states in the system. The impact of these results on the performance of the optically pumped Hg laser is discussed.
Electronic structure of Li–H2O and related neutral molecular complexes, including Al–H2O
Authors: Trenary Michael , Schaefer Henry F. , Kollman Peter A.
Published: February 2003

A b initio molecular electronic structure theory has been applied to a novel class of molecular complexes, of which the neutral Li–H2O may be considered the prototype. Near the Hartree–Fock limit Li–H2O is bound by 10.4 kcal/mole relative to separated Li+H2O. Electron correlation was accounted for by large configuration interaction, and this increases the predicted dissociation energy De(Li–H2O) to 11.7 kcal. A number of related molecular systems have been investigated including Al–H2O, predicted to be bound by 4.4 kcal.
Quantum mechanical reactive scattering via exchange kernels: Application to the collinear H+H2 reaction
Authors: Garrett Bruce C. , Miller William H.
Published: February 2003

A formulation of quantum mechanical reactive scattering given by Miller is applied to the collinear H+H2 reaction. The approach is the direct analog to the Hartree–Fock method of electronic structure theory, and it obviates the need for specialized (e.g., ’’natural’’ collision) coordinates. The rearrangement process takes place via an explicit exchange interaction (cf. electron exchange in Hartree–Fock theory), and closed channels are incorporated via a square-integrable set of correlation functions. Agreement with results obtained by others using other methods is excellent, showing this approach to quantum mechanical reactive scattering to be a viable one.
Vibrational energy relaxation of diatomic molecules isolated in rare-gas matrices: Role of orientational motions
Authors: Diestler D. J. , Knapp E. -W. , Ladouceur H. D.
Published: February 2003

A quantum-mechanical model which accounts for the dynamical role of orientational motions in vibrational energy relaxation (VER) of diatomic impurities isolated in rare-gas solids is developed. A simple closed expression for the VER rate constant is derived upon the following principal assumptions: (i) the lattice is planar, the diatomic a plane vibrotor; (ii) dynamical participation of local translational and bulk lattice modes is neglected. Results for the systems NH and ND in Ar, OH and OD in Ne, HCl and DCl in Ar and CO in Ar are in reasonable agreement with experiment. In particular, observed isotopic effects seem to be well described by the model. However, there are a couple of discrepancies between calculated and observed ratios of VER rate constants for the systems NH, ND/Kr and HCl, DCl/Ar. It is surmised that these are due to features not included in the model, e.g., lattice imperfections, van der Waals molecule formation and/or rotational–translational coupling.
Vaporization, thermodynamics, and dissociation energy of gadolinium monosulfide: Systematics of vaporization of the rare earth monosulfides
Authors: Fries James A. , Cater E. David
Published: February 2003

Mass spectrometric studies of the congruent, near-stoichiometric sublimation of gadolinium monosuflide and of the isomolecular gaseous reaction GdS+Y=Gd+YS have been carried out in the range 2005 to 2290 K. Sublimation occurs simultaneously to GdS molecules and to atoms Gd+S. Partial pressures are given by log PGd(atm) =−(29873±182)/T+(7.254±0.084) and log PGdS(atm) =−(30343±221)/T+(7.281±0.102). The indicated uncertainties are standard deviations; the absolute pressures may be low by as much as a factor 2. Enthalpies derived from combined second and third law considerations, with estimated maximum uncertainties due to cross section ratios, ground state degeneracies, and the use of the YS/GdS equilibrium for pressure calibration are (all in kcal/mole): GdS(s) =GdS(g), ΔH°2150=140±3, ΔH°0=147±4; GdS(s) =Gd(g)+S(g), ΔH°2150=270±4, ΔH°0=272±4; GdS(g) =Gd(g)+s(g), ΔH°2150=129.8±2.5, D°0(GdS) =125.0±2.5; Gd(s)+S(rh) =GdS(s), ΔH°298=−111±4. Data on the vaporization behavior and thermodynamics of the rare-earth monosulfides from LaS to GdS are assembled and/or estimated and discussed. Heats of atomization of MS(s) and of dissociation of MS(g) follow closely the trend of heats of sublimation of the metals. Heats of formation and sublimation of MS(s) are essentially equal for all the elements.
Electronic structure of CaO. I
Authors: Bauschlicher Charles W. , Yarkony David R.
Published: February 2003

Electronic wavefunctions for 15 states of CaO arising (nominally) from six electron occupancies are calculated at the single configuration (sc) SCF level and analyzed qualitatively in terms of Mulliken populations and an approximate overlap criterion. The accuracy of the sc approximation is assessed and shown to be highly inadequate in several cases. Approximate Te’s are extracted from these results when warranted by the quality of the sc wavefunctions. An improved two configuration wavefunction for the lowest 1Σ+ state is also determined and discussed in detail.
Molecular symmetry. II. Gradient of electronic energy with respect to nuclear coordinates
Authors: Dupuis Michel , King Harry F.
Published: February 2003

Symmetry methods employed in the HONDO ab initio polyatomic SCF program are extended to the analytic computation of energy gradients. Validity of the Hellmann–Feynman theorem is not assumed, i.e., all two-electron contributions to the gradient are included explicitly. The method is geared to the efficient computation of entire blocks of two-electron integrals. Just one of a set of symmetrically related blocks must be computed. The gradient contribution from each unique block is multiplied by q4, the number of equivalent blocks, and added into a ’’skeleton gradient vector,’’ all other blocks are simply omitted. After processing molecular integrals, the true gradient vector is generated by projecting the symmetric component out of the skeleton vector. The analysis is based on Eqs. (26) and (33) which are valid for many variational wavefunctions including restricted closed shell and unrestricted open shell self-consistent field functions. We also extend the use of translational symmetry proposed previously by Morokuma et al. To illustrate the method, the gradient of the restricted SCF energy is computed for eclipsed ethane using a Pople-type 63lG** basis and D3h symmetry. The same calculation is repeated using various subgroups of D3h. Computation times for SCF and for the gradient are each roughly inversely proportional to the order of the group, and for a given symmetry, the gradient computation takes about two and a half times as long as SCF.
Effective core potentials for the cadmium and mercury atoms
Authors: Basch Harold , Newton M. D. , Jafri J. , Moskowitz J. W. , Topiol S.
Published: February 2003

A b initio effective core potentials have been obtained for the cadmium and mercury atoms by the methods of Kahn et al., [J. Chem. Phys. 65, 3826 (1976)]. Both two and twelve valence electron representations of Cd and Hg were tested for various atom state-configurations by comparison with all-electron calculations. The generated potentials were used to obtain the equilibrium bond distances and molecular binding energies for the dichloride and dimethyl compounds of both atoms from single and optimum-double configuration self-consistent field calculations.
Generalized effective Hamiltonians: Time scale separation within a semiclassical formalism
Authors: DePristo Andrew E. , Rabitz Herschel
Published: February 2003

A theory for collision-induced transitions in the subset of quantum states ‖ae〉 is developed, where the full molecular basis is ‖aeau〉. The only assumption is that changes in au occur much more quickly than those in ae. The choice of ae and au is in general arbitrary, and it is shown how to make this separation based on the type of experimental measurement under consideration. For example, an evaluation of an atom–vibrotor problem (i.e., ae=n, au=jmj) is considered. In conjuction with this illustration an analysis of the breathing sphere (BS) approximation is carried out. It is concluded that a modified BS method (i.e., use of the diagonal rotational potential) should be valid when the random phase approximation holds for the rotational scattering amplitude.
All-electron nonempirical study of the ground state of MgF2
Authors: Pendergast Phil , Hayes Edward F.
Published: February 2003

LCAO–MO–SCF calculations on the ground state of MgF2 are reported for a number of geometries (both linear and bent). The results indicate a linear molecule with an equilibrium bond length (Mg–F) of 1.77 Å. All three force constants for the molecule are predicted. Least squares fitting of the data to second order potential functions gives force constants fr=3.21, frr=−0.029, and fϑ/r20=0.188 mdyne/Å. Dipole moment calculations for a number of geometries, and the diamagnetic susceptibility tensor, quadrupole tensor, and other molecular properties for the lowest energy conformation are reported.
Microwave optical double resonance spectrum of NH2. IV. Observation of an unusual rotational transition in ? 2B1
Authors: Hills G. W. , Lowe R. S. , Cook J. M. , Curl R. F.
Published: February 2003

Two rotational transitions in the ground 2B1 state of NH2—331, J=7/2←413, J=7/2 and 331, J =7/2←413, J=9/2—have been observed by microwave optical double resonance. The transitions are magnetic dipole allowed as a result of the spin–rotation interaction mixing of 413, J=7/2 with 331, J=7/2. An analysis of the mixing when combined with the previously determined spin–rotation centrifugal distortion parameters allows the determination of five of the six linearly independent spin–rotation centrifugal distortion constants. The resulting constants (in MHz) are ηaaaa=30.7(6), ηbbbb=0.624(14), ηaabb=−2.7(14), ηbbaa=−13.9(14), and (ηabab+ηabba)/2=3.4(2), where the quoted error in parentheses is three standard deviations.
Heterogeneous recombination of nitrogen atoms by the Smith side tube method: Effects of tube length and homogeneous recombination
Authors: Shuman M. E. , Brennen W.
Published: February 2003

An apparent pressure dependence of the derived catalytic activity of Pyrex for recombination of nitrogen atoms was observed in a series of Smith side tube experiments. The pressure dependence is shown to arise from an improper application of the infinite cylinder approximation. The effect of homogeneous recombination on the modeling of Smith side tube experiments is explored numerically.
OODR spectroscopy of BaO. II. New observations of a 3Π and A′ 1Π and re-examination of the Parkinson band system
Authors: Gottscho Richard A. , Koffend J. Brooke , Field Robert W. , Lombardi John R.
Published: February 2003

One and two dye lasers have been used in an optical–optical double resonance (OODR) study of the excited B 1Π and C 1Σ+ states as well as the low-lying, long-lived A′ 1Π and a 3Π1 electronic states of BaO. C 1Σ+ (v=0) is shown to be the upper level in the v′=0 progression of the Parkinson band system. Intensity anomalies in C 1Σ+–X 1Σ+ emission, due to an interference effect between parallel and perpendicular transition amplitudes, have proved to be a sensitive indication of ΔΩ=±1 perturbations. Emission from C 1Σ+, which is populated by absorption of two photons via a real intermediate A 1Σ+ vibronic level, into A′ 1Π (v=0,1, and 2) and a 3Π1 (v=0,1, and 2) has been observed. A scheme is presented by which the relative populations of the A′ 1Π and a 3Π ’’reservoir states’’ could be monitored.
Measurement of chlorine atom diffusion
Authors: Judeikis Henry S. , Wun Marilyn
Published: February 2003

Chlorine atom diffusion coefficients in argon were determined using a flowing afterglow system and electron spin resonance detection. Measured values, projected to 1 atm total pressure and 295°K, were 0.26±0.05 cm2/sec. Measurements were also made of oxygen atom diffusion in helium for comparison to previously reported values for the latter system. Diffusion coefficients for oxygen atoms in helium, projected to 1 atm total pressure and 295°K, were found to be 1.08±0.12 cm2/sec in this study, compared to literature values of 1.00 and 0.72 cm2/sec.
Estimate of the inversion barrier in SbH3
Authors: Marynick Dennis S. , Dixon David A.
Published: February 2003

A b initio self-consistent field calculations have been performed on the planar and pyramidal forms of SbH3. A slater orbital basis set Sb(1s,2s,3s,4s,4s′, 4s″,2p,3p,4p′, 4p″, 3d,3d′, 4d,4d′,4d″) and H(1s2s2p) was employed, and the calculated barrier is 46.2 kcal/mole. A discussion of the use of split valence Slater orbital basis sets is also present.