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 S₀ were measured for incident CH₄ prepared both with a single quantum of ν₃ antisymmetric stretch vibration by infrared laser pumping and without laser excitation. Vibrational excitation of the ν₃ mode is observed to be less efficient than incident translational energy in promoting the dissociation reaction with a vibrational efficacy η^ν = 0.65. The initial state resolved sticking coefficient S₀^ν was found to be independent of the surface temperature over the 50 kJ/mol to 120 kJ/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.