Photodissociation Dynamics of tert-Butyl Nitrite on Ag(111): Characterization of Translationally and Internally Excited NO Fragments

摘要

The translational, vibrational, and rotational characteristics of nitric oxide, NO, ejected by 351 nm photodissociation of tert-butyl nitrite, (CH_3)_3CONO, adsorbed on Ag(111) have been investigated using resonance-enhanced multiphoton ionization time-of-flight (REMPI-TOF) and interpreted using a direct excitation and collisional relaxation model. There are three translational energy components denoted as collisionless, intermediate, and thermalized. The collisionless component has characteristics matching those found for gas phase monomer photolysis. The thermalized component has characteristics expected for NO accommodated to the substrate temperature, while the more complex intermediate component is qualitatively describable in terms of collisions of nascent energetic NO with surrounding species as it exists into the gas phase. There are strong v" = 1 and 2 but negligible v" = 0 contributions to the collisonless component. The collisonless component is also characterized by high rotational excitation; Gaussian rotational distributions with J_(max) = 24.5 ± 1 for v" = 1 and 29.5 ± 1 for v" = 2 provide reasonable fits. The translationally thermalized component is dominated by the v" = 0 vibrational state and by a Boltzmann rotational distribution (T_(rot) = 124 ± 30 K); i.e., all three modes of motion are thermalized. The vibrational and rotational characteristics of the intermediate translational component are more complex and will require simulation and angle-resolved REMPI for fuller elucidation.