State-resolved dynamics of NO produced by photodissociation of t-butyl nitrite on Ag(111)

The dynamics of nitric oxide, NO, produced by 248 nm photodissociation of t-butyl nitrite, (CH3)3CONO, adsorbed on Ag(111) has been probed using resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) and interpreted using a direct excitation and collisional relaxation model. NO TOF spectra vary with rotational state and surface coverage, submonolayer to multilayers, of t-butyl nitrite. High rotational state (J>40.5) spectra show a sharp peak of fast NO, interpreted as collisionless ejection, along with an intermediate speed peak ascribed to NO that has collided with neighbors. The collisionless peak is evidence supporting direct excitation followed by prompt ejection of NO. As J is lowered from 50.5 to 12.5, the intermediate peak position drops from 60 to 30% of the collisionless kinetic energy. Low J (< ∼20.5) spectra show a slow peak thermalized to the surface temperature and interpreted as NO produced by direct photolysis but momentarily trapped at the surface. There is no evidence of any significant contributions from either substrate-mediated excitation or surface quenching.