Quantum state resolved molecular beam reflectivity measurements: CH4 dissociation on Pt(111)

The King and Wells molecular beam reflectivity method has been used for a quantum state resolved study of the dissociative chemisorption of CH4 on Pt(111) at several surface temperatures. Initial sticking coefficients were measured for incident CH4 prepared both with a single quantum of antisymmetric stretch vibration by infrared laser pumping, and without laser excitation. Vibrational excitation of the mode is observed to be less efficient than incident translational energy in promoting the dissociation reaction with a vibrational efficacy = 0.65. The initial state resolved sticking coefficient was found to be independent of the surface temperature over the 50kJ/mol to 120kJ/mol translational energy range studied here. However, the surface temperature dependence of the King and Wells data reveals the migration of adsorbed carbon formed by CH4 dissociation on the Pt(111) surface leading to the growth of carbon particles.