Dissociative sticking of CH4 on Ru(0001)

Abstract

In this study the CH 4 dissociation probability on Ru͑0001͒ is found for various translational and vibrational energies. The absolute sticking values are determined from King and Wells experiments and carbon uptake curves. The carbon amount is determined from the recombination signal of carbon with oxygen obtained after the beam exposure when heating in an oxygen atmosphere. The measured sticking coefficient of CH 4 is strongly enhanced both by increasing the translational and the vibrational energy of the CH 4 molecule. A model is applied to the data and an estimate of the thermal activation energy for CH 4 dissociation is found to be in good agreement with previous bulb experiments.

A note on the vibrational efficacy in molecule-surface reactions

“…This has now been reported for a number of systems, CH 4 /Ni(111) [23,24], CH 4 /Ni(100) [25], CH 4 /Ru(0001) [26] and even for the "simple" N 2 /Ru(0001) [27,28] case. Several hypotheses have been proposed in order to explain the "surprising" results Θ vib (R) > 1: It has been suggested that if the asymptotic reactivity (i.e., the saturation value of the dissociation probability) increases for vibrationally excited molecules, then Eq.…”

Bond breaking in vibrationally excited methane on transition-metal catalysts

“…A number of molecular beam experiments in which the dissociation energy was measured as a function of translational energy have observed that vibrationally hot CH 4 dissociates more readily than cold CH 4 , with the energy in the internal vibrations being about as effective as the translational energy in inducing dissociation. [1][2][3][4][5][6][7] Two independent bulb gas experiment with laser excitation of the 3 asymmetrical stretch and 2 4 umbrella modes on the Rh͑111͒ surface, 8 and laser excitation of the 3 and 2 3 modes on thin films of rhodium 9 did not reveal any noticeable enhancement in the reactivity of CH 4 . A recent molecular beam experiment with laser excitation of the 3 mode did succeed in measuring a strong enhancement of the dissociation on a Ni͑100͒ surface.…”

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

“…Some experiments have also observed that vibrationally hot CH 4 dissociates more readily than cold CH 4 , with the energy in the internal vibrations being about as effective as the translational energy in inducing dissociation. [2][3][4][7][8][9][10]13 A molecular beam experiment with laser excitation of the 3 mode did succeed in measuring a strong enhancement of the dissociation on a Ni͑100͒ surface. However, this enhancement was still much too low to account for the vibrational activation observed in previous studies and indicated that other vibrationally excited modes contribute significantly to the reactivity of thermal samples.…”