Near-threshold vibrational excitation ofH2by electron impact: Resolution of discrepancies between experiment and theory

New measurements and calculations of near-threshold (0.5–5.0 eV) e-${\mathrm{H}}_2$ vibrational-excitation cross sections challenge previous determinations based on transport analysis. Elastic and ${\mathit{v}}_0$=0→v=1 cross sections measured in a crossed electron-molecular-beam apparatus agree well with values calculated using a vibrational close-coupling theory with a separable represetnation of exchange, particularly at energies below 2.0 eV, but are incompatible with cross sections derived via analysis of electron-swarm transport data.