Barry I. Schneider

R-matrix theory for electron-atom and electron-molecule collisions using analytic basis set expansions

Abstract A formulation of R-matrix theory based on analytic basis set expansions of the internal wavefunction is presented which has several advantages over the more conventional approach. Integral evaluation is simple even for diatomic molecules, the R-matrix boundary condition is incorporated into the hamiltonian not the basis functions and single-center expansions are eliminated for non-spherical targets. Results for electron-He scattering are presented and compared with other calculations to illustrate the technique.

The coupled channel R‐matrix propagation method

Using a Green’s function approach, we present an alternate derivation of the R‐matrix propagation equations. We also present an extension of the method which employs a basis set expansion for both translational and target motions within each R‐matrix sector. This new approach is then investigated in comparison to the original close‐coupling approach, studying a model collinear vibrational excitation problem. The new approach allows much larger R‐matrix boxes to be used in regions of configuration space where the potential is changing rapidly with the scattering coordinate.

Multireference many‐body perturbation theory: Application to O2 potential energy surfaces

A modification of multi‐reference many‐body perturbation theory is introduced and applied to potential surface calculations of the first 3Σ−g, 1Δg, and 1Σ+g bound states of O2. The modification enhances the convergence and efficiency of both Rayleigh–Schrodinger and Brillouin–Wigner expansions by pre‐diagonalizing the primary space and then contracting to a smaller dimension space before calculating perturbative corrections.

Study of the potential curves of xenon with other rare gas atoms

The model for the forces between closed shell atoms recently developed by Gordon and Kim is applied to the ground state potential energy curves of Xe–Xe, Xe–He, Xe–Ne, Xe–Ar, and Xe–Kr. Agreement between experimentally determined values of the distance between the nuclei at the potential minimum and the depth of the potential well is quite good considering the simplicity of the calculation.

Interaction potentials for UF6 with itself and with rare-gas atoms

Abstract Potential curves have been calculated for the UF 6 -UF 6 and UF 6 -rare gas atom interactions using statistical models for the UF 6 charge density and the intermolecular interaction. Agreement with available experimental data is good.

Dissociative attachment of electrons to F2

The rate of dissociative attachment of electrons to F2 in mixtures with N2 and Ar has been measured over the electron mean energy range 0.9–4 eV. The results show that the rate is about 7×10−9 cm3/s at a mean energy of 1 eV, and decreases with increasing electron mean energy as (mean energy)−3/2.

AB-initio effective potentials derived from many-body green's function theory: Application to Li

Abstract The many-body Greens function technique, developed by Schneider, Taylor and Yaris for electron scattering problems, is applied to the calculation of ab-initio effective potentials (pseudo-potentials) in atoms and molecules. Computational results on the ionization potentials, excitation energies and bound-bound oscillator strengths in lithium show quantitative agreement with experiment and contain all the heuristically expected physical effects.

Pseudostates and low-energy electron-molecule collisions: applications to H2 and N2

Abstract A simple procedure for generating pseudostates for low-energy electron-molecule collisions is described which requires only a standard Hartee-Fock program. The technique uses an additional nuclear center to simulate the distortions of the charge cloud of the molecule by a low-energy electron. Calculations are presented for H 2 and N 2 which show that accurate pseudo-orbitals can be obtained by the method. A simple application of the pseudo-state orbitals for low-energy e + H 2 scattering gives results which are in very good accord with experiment and represents the first ab initio treatment of both electron exchange and polarization in an electron-molecule collision.

The solution of driven equations by R‐matrix propagation methods

A method for the solution of the inhomogeneous (driven) Schrodinger equation is presented which is a generalization of the R‐matrix propagation technique developed by Light and Walker. The method is numerically stable and allows the direct calculation of transition matrix elements for photodissociation (or photoionization) from the asymptotic form of the wave function. Thus, no additional integrals need to be computed. The method makes direct contact with the work of Freed et al. and Heller and demonstrates that straightforward modifications of standard collision theory can be used for the half‐collision problem.

The use of gaussian basis functions in fredholm calculations of electron-atom and electron-molecule collisions

Abstract A simple modification of the usual Fredholm procedure for the calculation of electron scattering cross sections is described which makes use of the properties of gaussian type orbitals. The difficulties associated with the evaluation of bound-free and free-free integrals of the hamiltonian are eliminated. The technique may be extended to the electron-molecule scattering problem quite easily and makes the calculation of electron-molecule scattering cross sections a practical procedure.