Paper SS-TuP13
Surface Temperature Dependence of Methane Dissociation on Ni

Tuesday, October 16, 2007, 6:00 pm, Room 4C

The past decade has seen major groundbreaking work in the understanding of the role vibrational energy plays in the dissociation of methane on nickel surfaces. Yet, little work has been done on developing an understanding of the effect of surface temperature on this reaction. Two questions remain regarding the energy contained in the surface: First, how does the thermal bath of the surface atoms couple to the reaction coordinate? Second, does dislocation of the surface atoms alter the distribution of barriers to dissociation? Recent theoretical work suggests that the system is able to access lower barriers when the surface atoms are displaced above the plane of the surface. A change in the location of the Ni surface atom below the incident methane molecule could result in a lower energetic barrier making the reaction much more probable. As the surface temperature is increased, the probability of the incident methane molecule impacting on a displaced Ni atom increases. Experimentally, the biggest hurdle in understanding the dynamics that surface temperature plays in reactivity is deconvolting the gas-phase dynamics from the surface temperature dynamics. In thermal bulb experiments, it is not possible to discern the role of energy in the gas-phase comparatively to that of energy of the surface. Supersonic molecular beam experiments allow independent control of both the surface temperature, the impact energy and the average vibrational energy of the incident gas-phase molecules. Additionally, we use a narrow-bandwidth IR laser to prepare a non-equilibrium distribution of vibrational states, which allows us to determine the reactivity of select rovibrational eigenstates of the methane molecules over a range of incident kinetic energies and surface temperatures. The overall goal of these experiments is to determine the coupling of the vibrationally excited methane molecules to the phonon bath of the surface atoms and see what impact different surface temperatures have on reactivity.