Photodissociation at 193 nm of tert-butyl nitrite on Ag(111)

The translational and internal state properties of nitric oxide, NO, ejected by 193-nm photodissociation of tert-butyl nitrite, (CH3)(3)CONO, TBN, adsorbed on Ag(111) have been investigated using resonance-enhanced multiphoton ionization time-of-flight (REMPI-TOF) and quadrupole mass spectrometer time-of-flight (QMS-TOF). The results are described in terms of three components depending on the number of collisions along the exit trajectory and are compared to prior work using 248- and 351-nm photons. Although 193-nm photons have higher energy, the characteristic translational energy of the collisionless NO (0.55 eV) lies between that for 248 nm (0.89 eV) and 351 nm (0.39 eV). As for gas-phase photolysis at 193 nm, the NO is rotationally cold (J(max) = 15.5), much lower than for both 248- (J(max) = 53.5) and 351-nm (J(max) = 31.5) photolysis. The NO vibrational distribution is dominated by upsilon" = 1, whereas upsilon" = 0 for 248 nm and upsilon" = 1 and 2 for 351 nm photodissociations, respectively. Angle-resolved REMPI-TOF and QMS-TOF studies give information about the orientation of adsorbed TBN. While TBN is more stable with the C-O-N=O plane perpendicular to surface and the internal O-N bond directed about 40degrees away from the surface normal, dosing less than a full monolayer at 80 K does not achieve this state fully. Annealing to 110 K is sufficient to realize this molecular orientation. For multilayer coverage dosed at 80 K, the data are consistent with considerable surface roughness compared to a surface annealed at 110 K.