Arnold Russek

The HeH2 energy surface

A composite ab initio energy surface is obtained for the HeH2 triatomic molecular system by combining earlier calculations that covered parts of the surface. The extended surface covers the full angular range of He relative to the H–H axis as well as the full range of He–H2 separations. As with all calculations thus far, the extended ab initio energy surface covers only a narrow range of H–H separations in the vicinity of 1.4 a.u., the equilibrium separation of ground state H2. In addition, a new parametric representation of the ab initio energy surface is developed in terms of simple analytic functions based on the physics underlying the three principal interaction mechanisms responsible for the energy surface, and collisional applications are discussed briefly. All of the interaction mechanisms give rise to three‐body interaction terms, an understanding of which is crucial to interpreting the behavior of the energy surface. This parametric representation reproduces the ab initio calculated values with a...

Ab initio (HeH2)+ energy surfaces and nonadiabatic couplings between them

The energy surfaces of the three lowest adiabatic states of the (HeH2)+ triatomic molecular system have been calculated ab initio as functions of all three variables describing the triatomic geometry, using the BRLJHU set of quantum chemistry programs. The procedure is described by the acronym SA‐MCSCF/CI, for state‐averaged multiconfiguration self‐consistent‐field calculation, followed by a full configuration interaction calculation. In addition the nonadiabatic matrix elements which couple these adiabatic states have been calculated. Results have been obtained on a sufficiently fine mesh for interpolation by a spline‐fit program to produce energy differences and nonadiabatic coupling matrix elements over the full mesh required for collisional excitation problems of He+ on H2 and H+2 on He involving these states.

Dissociating states of the H−3 system

Single determinant Hartree–Fock calculations for the lowest singlet and triplet potential energy surfaces of the H−3 system are presented over a broad range of isosceles triangular configurations of the nuclei. The addition of a diffuse s function to the four‐term Gaussian expansion of Huzinaga for H(1s) together with p type polarization functions produces results which are in agreement with experiments on double electron capture by H+3 to form H−3. The present calculations predict that capture to the ground singlet state produces H2+H−, with a dissociation energy in reasonable agreement with the experimental findings. Capture to the triplet state is predicted to resulted in the three body dissociation H+H+H− with small dissociation energy. This is consistent with, but not positively confirmed by, the experimental data.