An ab initio treatment of near-threshold vibrational excitation of H₂by electron impact: new perspectives on discrepancies between crossed-beam and swarm data

New crossed-beam measurements of the vibrational excitation cross section of H 2 are at variance with earlier determinations based on analysis of swarm data. This discrepancy poses a dilemma, as the modeling of a variety of plasma processes depends on cross sections derived from transport analysis. The authors present calculated cross sections for vibrational excitation of H 2 by low-energy electron impact using a fully ab initio treatment of the electronic motion with incorporation of nonadiabatic nuclear effects through an approximate off-shell T-matrix formalism. The authors' cross sections are in good agreement with recent data and are substantially larger than the values deduced from swarm data.