Electron-Induced Desorption of Physisorbed H2 via Resonance Vibrational Excitation

We show by electron energy-loss measurements that desorption of physisorbed H-2 and D-2 induced by low-energy electrons takes place with large cross sections, predominantly via resonance excitation of the molecule-surface vibrational mode. The observed H-2, D-2 cross-section ratio supports a picture where rotation-translation conversion of the resonance excited j=0 -> 2 rotational transition contributes to the desorption of H-2, while this channel is energetically closed for D-2.