N 2 dissociative adsorption on Ru(0001): The role of energy loss

Abstract

New molecular beam experiments on the dissociation probability S 0 for N 2 on Ru͑0001͒ are presented. These are in general agreement with prior measurements and exhibit very unusual behavior; a very slow increase of S 0 with incident kinetic energy E and the fact that S 0 is still only ϳ10 Ϫ3 at incident energies considerably above the barrier. A simple dynamical model is developed to describe this unusual sticking behavior. The key aspect is that there is considerable energy loss ⌬ from E upon initial impact with the surface ͑principally to the lattice͒ and only EϪ⌬ is then available to surmount the activation barrier in the exit channel. Using experimentally measured values of ⌬ from scattering experiments gives good qualitative agreement of this model with the measured S 0. One implication of the strong energy loss is that there is an apparent violation of detailed balance when comparing only the reactive fluxes of activated adsorption and associative desorption.

A note on the vibrational efficacy in molecule-surface reactions

“…As it was shown in Refs. 30 and 31, these theoretical results reproduce the surprisingly low dissociation probabilities [27,[50][51][52] found in the experiments. The results can be understood based on the very special characteristics of the N 2 /Ru(0001) PES: [28,30,31,51] The minimum barrier is very high, around 2.3 eV, and the PES displays high anisotropy and corrugation, i.e., small changes in the orientation and/or the position of the molecule gives rise to large changes in the potential energy (see Fig.…”

Multidimensional Effects on Dissociation ofN2on Ru(0001)

“…Our calculations suggest that neglect of the v 2 contribution [the experiments [10] were done for only 2 T n values] should lead to overestimation of the experimental by no more than 0.5. Both the present adiabatic theory and previous experiments [10] thus show a large effect of N 2 vibration on dissociation on Ru(0001), in contrast to a previous statement [14] that the effect should be less than for H 2 =Cu ( 0:5).…”

“…Continuous lines with full symbols represent 6D adiabatic calculations, the dashed line with full symbols represents 2 1D adiabatic calculations from [11], and the dashed line with open symbols 2 2D nonadiabatic calculations from [11]. Experimental measurements: full circles from [10]; full green diamonds from [10]; full red squares from [14]. The inset shows S 0 times 10 2 vs normal translational energy.…”

“…An unusual feature of reaction of N 2 on Ru(0001) is that the dissociation probability (S 0 ) saturates at a very small value (10 ÿ2 ) for incidence energies E i V [10,14]. To understand the surprisingly low reactivity a combination of experiment and modeling analysis was applied [11].…”

The reaction rate for dissociative adsorption of N2 on stepped Ru(0001): Six-dimensional quantum calculations

“…52 Due to its importance, the N 2 -Ru system has been extensively studied experimentally. [53][54][55][56][57][58][59][60] Density-functional theory ͑DFT͒ calculations 52,61-65 explored the electronic structure and the reaction path.…”