NON-ADIABATIC EFFECTS IN THE HIGH-ENERGY SCATTERING OF NORMAL HELIUM ATOMS
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Date
1963
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Ohio State University
Abstract
“There is a large discrepancy $(\sim 9$ e.v.) between the calculated adiabatic electronic energy of the ground state $(X^{1} \Sigma_{g}^{+})$ of the system $He_{2}$ and the effective scattering potential deduced from experiments with high-energy (2 kev) atomic helium beams, at small interatomic distances (0.53 Angstrom). A theory of the potential including non-adiabacity is presented: the non-adiabacity arises from the high angular momentum of the ``measuring collisions’’. Perturbation theory is employed to give an estimate of the magnitude of non-adiabacity in agreement with the experimental discrepancy at 0.53 {\AA} and to predict the observed agreement of adiabatic theory and experiment at 1.06 {\AA}. A variational calculation is presented which gives about 25% of the discrepancy by inclusion of only a few discrete states. A pseudo-Hamiltonian is introduced as a means of including virtual continuum contributions, which are very important, and a description is given of calculations now under way to include the continuum. It is hoped that most of the discrepancy can be calculated variationally.”
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Author Institution: Department of Chemistry, Massachusetts Institute of Technology