CH4 dissociation on Ni(100): Comparison of a direct dynamical model to molecular beam experiments

Abstract

This paper makes an extensive comparison of a dynamical model for a mechanism of direct dissociation to the detailed molecular beam experiments of CH4 dissociation on a Ni(100) surface reported in the previous paper. When a PES incorporating an ‘‘exit channel’’ barrier is used in the model and steric (multidimensional) aspects are included approximately via a ‘‘hole’’ approximation, excellent agreement is achieved between the model and experiments. This strengthens the qualitative mechanistic conclusions of Holmblad, Wambach, and Chorkendorff [J. Chem. Phys. 102, 8255 (1995)].

Dissociative sticking of CH4 on Ru(0001)

“…The basis of the model used was to treat the methane molecule as a quasidiatomic molecule, consisting of a hydrogen atom and a methyl group so that the dissociation process only involved the breaking of the H-CH 3 bond. 18,19 Excitation of the vibrational stretch mode in this bond was assumed to be responsible for the enhanced sticking for increased nozzle temperatures. Using the ansatz previously applied for the CH 4 /Ni(100) system 10 we assumed that the sticking coefficient of methane with translational energy E trans and in the vibrational state would dissociate with the probability given by…”

“…In order to compare the result of the thermal experiment, a model is fitted to our measured absolute sticking coefficients and a thermal activation energy of 37 kJ/mol is found which is in good agreement with the bulb experiments by Wu et al 16 The model is based on work by Luntz et al where CH 4 is modeled as a quasidiatomic molecule. 18,19 This is previously applied successfully to the experimentally determined dissociation probabilities of CH 4 on Ni͑100͒. 10 This quasidiatomic assumption is also used as the basis in a recent work by Carré et al where the effect of allowing all molecular orientations of the incoming CH 4 molecule is investigated.…”

D2 dissociative adsorption on and associative desorption from Si(100): Dynamic consequences of an ab initio potential energy surface

“…However, the well depth is weakened and the equilibrium bond length stretched in a smooth fashion as the molecule approaches the surface. This form of a modified Morse potential has been defined previously; 26 …”

“…␣ is approximately the change in the classical threshold of the state of H 0 ͑r͒ with barrier height variation 26 and E is the incident energy. These approximations produce a rigid shift of the excitation profile with changes in barrier height.…”

Energy dissipation and scattering angle distribution analysis of the classical trajectory calculations of methane scattering from a Ni(111) surface

“…Wave packet simulations of the methane dissociation reaction on transition metals have treated the methane molecule always as a diatomic up to now. [15][16][17][18][19][20] Apart from one C-H bond ͑a pseudo 3 stretch mode͒ and the molecule surface distance, either ͑mul-tiple͒ rotations or some lattice motion were included. None of these studies have looked at the role of the other internal vibrations, so there is no model that describes which vibrationally excited mode might be responsible for the experimental observed vibrational activation.…”