Cross sections for the vibrational excitation of the H2 X 1Σ+g(v) levels generated by electron collisional excitation of the higher singlet states

Abstract

The excitation cross sections, σ(v,v″), for an H2 molecule initially in any one of the 15 vibrational levels, v belonging to the ground electronic state and excited to a final vibrational level, v″ are evaluated for direct excitations via all members of the excited electronic singlet spectrum. Account is taken of predissociation, autoionization, and radiative decay of the excited electronic spectrum that leads to a final population distribution for the ground electronic state, X 1Σ+g(v″). For v=0, account is taken explicitly of transitions via the B, C, B′, and D electronic states in evaluating the cross sections. The additional contribution of excitations via all Rydberg states lying above the D state enhances these cross sections by approximately 10%. For v≳0, cross sections are evaluated taking explicit account of transitions through the B and C states; higher singlet excitations enhance these values by 25%. The choice of the reference total cross sections remains a subjective one, causing the values calculated here to have a possible uncertainty of +20%−30%. For excitations occurring within a hydrogen discharge, collisional excitation-ionization events among the intermediate singlet states will effectively quench the v, v″ excitation process for discharge densities in excess of the range 1015–1016 electrons/cm−3.