Photodissociation dynamics of tert-butyl nitrite on Ag(111): Characterization of translationally and internally excited NO fragments

The translational, vibrational, and rotational characteristics of nitric ox ide, NO, ejected by 351 nm photodissociation of tert-butyl nitrite, (CH3)(3 )CONO, adsorbed on Ag(lll) have been investigated using resonance-enhanced multiphoton ionization time-of-flight (REMPI-TOF) and interpreted using a d irect excitation and collisional relaxation model. There are three translat ional energy components denoted as collisionless, intermediate, and thermal ized. The collisionless component has characteristics matching those found for gas phase monomer photolysis. The thermalized component has characteris tics expected for NO accommodated to the substrate temperature, while the m ore complex intermediate component is qualitatively describable in terms of collisions of nascent energetic NO with surrounding species as it exits in to the gas phase. There are strong v " = 1 and 2 but negligible v " = 0 con tributions to the collisionless component. The collisionless component is a lso characterized by high rotational excitation; Gaussian rotational distri butions with J(max) = 24.5 +/- 1 for v " = 1 and 29.5 +/- 1 for v " = 2 pro vide reasonable fits. The translationally thermalized component is dominate d by the v " = 0 vibrational state and by a Boltzmann rotational distributi on (T-rot = 124 +/- 30 K); i.e., all three modes of motion are thermalized. The vibrational and rotational characteristics of the intermediate transla tional component are more complex and will require simulation and angle-res olved REMPI for fuller elucidation.