Quantum-resolved analysis of electronically-stimulated NO₂ dissociation on Pt(111)

The electronically-stimulated dissociation of NO₂ on Pt(111) has been studied through state-selective, time-of-flight detection of the NO product above the surface. The NO leaves as a direct dissociation product resulting from 5-800 eV electron impact, whereas the O atom remains on the surface. The quantum-resolved analysis of the NO reveals fundamental aspects of the stimulated surface process such as dominant excitation channels and dynamics. Because of rapid decay via resonant tunneling from substrate levels, the 3 eV shallow valence excitations prominent in gas-phase photodissociation of NO₂ have lifetimes that are too short to produce observable dissociation on the metal surface. Instead, we find a 10-15 eV threshold which corresponds to ionization of 3b₂ and double ionization of 1a₂ levels which cannot be resonantly filled by substrate electrons and thus have the longest lifetimes relative to Auger decay. Screening of the hole(s) by the metal through the 6a₁ orbital of the molecule not only determines the lifetime, but is found to influence the extent of internal excitation in the NO product.