Trimodal velocity distributions of nitric oxide for ultraviolet photodissociation of CH3ONO adsorbed on Ag(111)

The photodissociation of ⩽1.0 monolayer methyl nitrite adsorbed on Ag(111) has been studied by angle- and mass-resolved time-of-flight spectrometry. Irradiation with 248 or 351 nm photons leads to ejection of NO with three translational energy components; the fast component is peaked away from the surface normal. The angular distribution of the ejected NO depends on the initial coverage and photolysis wavelength. A direct excitation mechanism is invoked for all three components; the fast molecules are directly ejected, the intermediate speed molecules have undergone one collision, and the slow molecules have undergone several collisions.