Analyses of Recent Experimental and Theoretical Determinations of e–H₂ Vibrational Excitation Cross Sections: Assessing a Long-Standing Controversy

Abstract

During the last four years, we have undertaken a major effort to resolve a serious, long-standing discrepancy between various experimental and theoretical determinations of the cross section for the v₀ = 0 → v = 1 vibrational excitation of H₂. This effort has involved crossed electron-beam molecular-beam measurements of relative angular distributions, measurements of transport coefficients in mixtures of H₂ and various rare gases, and ab initio theoretical calculations using a vibrational close-coupling formalism with an exact treatment of non-local exchange effects. The discrepancy remains unresolved—a fact with potentially wide-ranging consequences for beam experiments, theory, and the unfolding of inelastic electron–molecule cross sections from swarm data. New analyses of the transport data and the application of a new method of extrapolating angular distributions beyond the range of measurement sheds light on this disagreement and its implications.