PHOTOLYSIS OF AZOMETHANE ADSORBED ON PD(111)

The photolysis of azomethane (CH3NNCH3) adsorbed on Pd(111) has been studied under ultrahigh vacuum conditions. Temperature programmed desorption (TPD) has been employed as an analytical tool to study the photolysis products and their thermal behavior, using line of sight sampling by the mass spectrometer. Both the chemisorbed monolayer and the condensed multilayer have been investigated. No photolysis is observed in the monolayer. In the multilayer, photolysis breaks the CN bond of azomethane, producing ·CH3 radicals and N2, a process analogous to that observed for gaseous azomethane. The N2 desorbs directly during photolysis at 87 K, as do some of the ·CH3 radicals which scavenge hydrogen and desorb as methane. For an initial azomethane coverage of 1-3 monolayers, these ·CH3 radicals also scavenge H atoms during TPD from thermally decomposing azomethane and desorb as methane above 150 K. Above an azomethane coverage of 3 monolayers, the ·CH3 radicals are observed to combine during TPD, desorbing as ethane. The reaction of photolytically generated ·CH3 radicals with chemisorbed deuterium atoms on Pd(111) has been observed to produce CH3D below 150 K. At photon energies above 4.0 eV, the mechanism of photolysis is probably electron transfer from the substrate to the multilayer azomethane. At photon energies between ~ 3.1 and 4.0 eV, the photolysis mechanism could be either electron transfer or intra-adsorbate excitation. © 1990.