Resonant inelastic scattering of electrons from gas-phase and physisorbed N2. A time-dependent approach

We report the results of a theoretical study in which time-dependent quantum wave-packets have been used to simulate the resonant vibrational excitation of N2 by electron impact. We have studied the dynamics on model potential energy surfaces (PESs) explicitly including both the electron-molecule and the intramolecular coordinates. Resonance parameters for the 2Πg state in N2− were chosen to agree with those obtained from fixed nuclei ab initio calculations, and the resulting vibrational-excitation cross sections are in excellent agreement with experiment. For the case of an N2 molecule physisorbed on a metal surface, the metallic image potential is known to broaden the resonance and lower its energy. The degree of broadening is estimated by fitting calculated cross sections to those obtained experimentally for N2 on Ag.