John Bentley

Volume polarization in reaction field theory

In continuum reaction field models of solvation, unconstrained quantum mechanical calculation of the solute electronic structure inevitably leads to penetration of some solute charge density outside the cavity and into the solvent dielectric region. This produces a rarely recognized or treated volume polarization that contributes in addition to the commonly considered surface polarization. In this work a new practical implementation is described for quantitatively evaluating both volume and surface polarization contributions to the solute-solvent interaction with an irregularly shaped cavity surface. For illustration, numerical results are presented on several representative small neutral, cation, and anion solutes. The volume polarization contributions to energies and dipole moments are found to be somewhat smaller than those from surface polarization, but not negligible. The results are also used to test several charge renormalization approaches that have been previously proposed in the literature. Comp...

Electronic‐energy exchange cross sections for Ar* (3P) and Kr(1S)

Differential cross sections for Ar* scattered by Kr are obtained at four relative kinetic energies, 60.6–156 meV. Location and shape of rainbow maxima, observed at all the energies, are used to determine parameters for a double‐Lennard‐Jones potential. The parameters, e=9.11±0.25 meV and rm=5.06±0.84 A, are the same as those for K+Kr and are substantially different from those of Ar+Kr. A second set of maxima, visible at all energies and caused by exchange of electronic energy from Ar* to Kr, are analyzed to determine electronic‐energy exchange cross sections. The cross sections together with those obtained from thermal‐energy quenching measurements are consistent with an increase from a threshold of 25 meV. Possible mechanisms for the electronic‐energy exchange are discussed.

Potential energy surfaces for excited neon atoms interacting with water molecules

A substantial body of experimental data on interactions of metastable rare gas atoms with water molecules exists, but models of the interaction process are lacking. In order to interpret experiments involving collisions of Ne* with H2O, molecular orbital calculations with configuration interaction have been carried out for the six three‐dimensional potential surfaces arising from interaction of Ne (2p53s 1,3P) with a rigid H2O molecule. Basis sets of roughly double zeta and double zeta plus polarization quality have been used. An attraction of 0.25 eV is found between Ne* and H2O at a neon–oxygen distance of 2.5 A, in good agreement with the structure calculated for a Na–H2O complex. Multipolar expansions of the lowest triplet potential surface are reported. Interpretation of Penning ionization electron spectra and some excitation transfer results are aided by the present surface. An electrostatic model is proposed to construct potential surfaces of the type presented here.

Determination of electronic energies from experimental electron densities

An electrostatic energy expression due to Politzer is used to calculate total electronic energies from experimentally determined charge density functions. When partitioned as suggested in this paper, Politzer’s expression is useful for indicating the effects of bond formation, and for diagnosing problems in the charge density function. Application to experimental charge density data for beryllium and diamond crystal is reported. Some binding energies are also calculated, but caution is recommended in interpreting these values.

Accurate width and position of lowest 1S resonance in H− calculated from real‐valued stabilization graphs

The use of real‐valued stabilization graphs for calculation of resonance energies and widths is considered in connection with the lowest Feshbach resonance state of H−, nominally (Φ2s)2. One problem that arises is the difficulty of generating stabilization graphs with well defined avoided crossings between the resonance state of interest and nearby interacting continuum states. For this purpose, criteria are developed for selection of basis sets and CI lists and for determination of suitable stabilization parameters. Another problem is the extraction of resonance parameters from the stabilization graph. We study one particular analytic continuation procedure recently proposed by Isaacson and Truhlar. Criteria for separation of physical from nonphysical solutions of the complex energy stationary point, for determination of the necessary numerical precision for the input real eigenvalues, and for other details of the method have all been examined. The results for H−, even with a modest Gaussian basis set an...

Collision‐induced atomic dipole moments

A multipole expansion procedure is given for obtaining collision‐induced atomic dipole moments from the molecular moments of a pair of atoms in a collision governed by the Pauli exclusion principle. Atomic moments are reported for He, Ne, Ar, and H, as determined from homonuclear diatomic wave functions. These are combined, via the distortion model of Smith [Phys. Rev. A 5, 1708 (1972)], to obtain molecular dipole moments for the heteronuclear collision pairs. The molecular dipole moments are in fair agreement with results of molecular orbital calculations. Limitations and extensions of the procedure are discussed.

Theoretical study of lithium cation interactions with hydrocarbon radicals

Abstract The nature of the interaction between lithium cations and hydrocarbon free radicals has been examined by electronic structure calculations at the HF/6–31 G ** and MP2/6–31 G ** levels. Bonding in the radical cation systems CH 3 Li + , C 2 H 5 Li + , 2-C 3 H 7 Li + , C 2 H 3 Li + , and C 3 H 5 Li + closely resembles that between lithium cations and closed-shell molecules.

Low‐energy differential elastic scattering of Ne* (3P) by Kr(1S)

Differential elastic cross sections for Ne* (3P) scattered by Kr are obtained at three relative kinetic energies, 64 to 74 meV. Location and shape of rainbow maxima, observed at all energies, are used to determine the well depth and potential minimum for a double‐Lennard‐Jones potential. The results, e=8.05±0.49 meV, and rm=4.91±0.64 A are similar to those for Na+Kr and are substantially different from those of Ne+Kr. A value of 2.11 A for the atomic radius of Ne* is obtained which is close to that previously reported for Na.

Atomic Multipole Expansions of Molecular Charge Densities. Electrostatic Potentials

The molecular electrostatic potential has been shown to be a very useful tool for understanding the reactivities of molecules with ions or polar molecules1 and the structure and energetics of intermolecular complexes, including hydrogen bonded complexes.2 The electrostatic potential can be obtained as the by-product of a molecular orbital calculation in the form of a large table of numbers.3 A considerable computational advantage would be obtained if this information could be compressed into analytical form, and a large amount of effort has gone into the search for appropriate representations. For instance, Bonaccorsi, Scrocco and Tomasi4 have shown how one can resolve molecular electrostatic potentials into sums of contributions from fragments within the molecule; the fragment contributions are approximately transferable, allowing one to construct the potential for a large molecule without first performing a molecular orbital calculation on that molecule. Kollman5 has also addressed the problem of obtaining the potential without a wave function and has produced a family of point-charge models for which the necessary inputs are experimental bond lengths, bond angles, and dipole moments, atomic electronegativities, and van der Waals radii. These point-charge distributions produce electrostatic potentials at suitable reference points which are in reasonable accord with the potentials obtained from wave functions.

Low‐energy elastic and electronic‐energy exchange scattering of He* by Kr

Differential cross sections for He* scattered by Kr are obtained at three relative energies, 63.6–82.3 meV. Location of rainbow maxima and ’’rapid’’ quantum oscillations, observed at all energies, are used to determine parameters for a double Lennard‐Jones potential. The parameters, e=8.0±0.6 meV and rm=4.8±0.25 A, are close to those for Li+Kr and are substantially different from those of He+Kr. The effects of direct electronic‐energy exchange scattering are observed as excess scattered intensities between 10° and 30° lab. These effects are compared to those arising from chemi‐ionization.