Electronically Nonadiabatic Vibrational Excitation of N2 Scattered from Pt(111)

Molecular beam surface scattering is used to compare vibrational excitation of N-2 molecules in collisions with clean Pt(111) and Au(111) surfaces under UHV conditions. Direct single-bounce collisions are dominant under all conditions of this work, as evidenced by narrow specular angular scattering distributions and translational incidence energy dependent rotational temperatures. N-2(v = 0 -> 1) vibrational excitation is observed for Pt(111), but not Au(111). The excitation probabilities, ranging from to similar to 10(-3), follow an Arrhenius surface temperature dependence and increase with translational incidence energy with zero threshold. The observations are the typical fingerprint of nonadiabatic vibrational excitation due to an electron mediated excitation mechanism, identified in previous work on NO and CO scattering from electron affinity of the N-2 molecule (EA = -2.3 eV) makes this observation surprising and we discuss possible mechanisms.