Paper SS2-MoM8
State-resolved Reactivity of Methane (ν₂+ν₄) on Ni(111)

Monday, October 31, 2011, 10:40 am, Room 110

Methane dissociation on transition metal surfaces is the rate-limiting step in the steam reforming reaction, which is the principal route for converting CH₄ to H₂. Understanding the dynamics of energy flow during this process has both fundamental and practical impact. Experiments that measure the reactivity of methane prepared in select vibrational states reveal how specific nuclear motions promote methane dissociation. State-resolved measurements for methane reactivity on Ni and Pt surfaces show that molecules prepared in vibrationally excited states are more reactive than those without laser excitation, and the efficacies of vibrational energy in different excited states can differ significantly.

Here, we present state-resolved reactivity measurements of the ν₂+ν₄ bending combination vibration of CH₄ on Ni(111) as a function of translational energy. This state is a member of the pentad of vibrational states that can play an important role in the thermal activation of methane. We are able to quantify the state-resolved reactivity of methane in this particular vibrational state over a wide range of translational energies. We compare the efficacy for ν₂+ν₄ bend with that of the ν₃ stretching and 3ν₄ bending states to gain insight into the ability of ν₂ excitation to promote dissociative chemisorption. The result permits a detailed comparison of the role of stretch and bend excitation of methane dissociative chemisorption on Ni(111).