Effect of collision energy and incidence angle on the precursor-mediated dissociative chemisorption of N2 on W(100)

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Abstract
The dissociative chemisorption of N2 on W(100) is found to fall rapidly with increasing kinetic energy Ei in the range 26 to 450 meV. For a surface temperature Ts of 300 K, the initial dissociative chemisorption probability S0 falls from ∼0.8 at Ei=26 meV to 0.15 at 450 meV. Over this range of energies the dissociation probability is also found to fall rapidly with Ts, and to be relatively insensitive to surface coverage at low Ts, strongly suggesting that dissociation occurs in this system via a precursor under these conditions. This picture is supported by angular distribution measurements of the scattered molecules which are consistent with an appreciable cosine component, which also becomes smaller as Ei increases. Results are found to be surprisingly insensitive to the incidence angle over the range 0° to 70°, indicating that the trapping process scales quite closely with the total incidence energy.