Photochemistry of methane on Cu(111)

The photochemistry of methane physisorbed on Cu(111) at 35 K has been investigated by temperature-programmed desorption (TPD). Methane is photodissociated into hydrogen, methylene, and methyl by 6.4 eV photon irradiation. Post-irradiation TPD showed new desorption peaks of ethylene at 115 and 380 K, in addition to the 430 K peak reported before. They are attributed to molecular desorption of ethylene photochemically formed from methane at 35 K, associative thermal recombination of two methylene groups, and thermal disproportional reactions of four methyl groups, respectively. The photoreaction cross-section of methane depletion is estimated to be 2.0×10−20 cm2.