The dynamics of NO scattering from NO- and CO-covered Ni(100)

Abstract

The dynamics of NO scattering from NO- and CO-covered Ni(100) has been investigated using supersonic molecular beam techniques and laser induced fluorescence (LIF). Angular distributions for NO scattering from NO-covered Ni(100) at a surface temperature of 140 K indicate a gradual change from trapping-desorption to direct inelastic scattering with increasing incident translational energy, E trans from 90 to 1100 meV. The internal energy distributions of the scattered NO in various geometries as a function of incident translational energy are also indicative of scattering into two channels. Adsorption kinetics for NO on initially clean Ni(100) exhibit precursor behavior at incident energies up to about 300 meV consistent with trapping into an extrinsic precursor state. NO efficiently displaces CO from a CO-saturated Ni(100) surface at a temperature of T s = 140 K. Initial displacement probabilities d 0 for NO on CO-covered Ni(100) are nearly as large as initial sticking probabilities s 0 for NO on clean Ni(100) ( d 0 = 0.53, s 0=0.67 at E trans=90 meV). The decline in d 0 with increasing E trans suggests that the displacement proceeds through a trapped intermediate. A very high trapping probability for the covered surface is concluded and the role of efficient energy transfer of the kinetic energy of the incident molecule to the low energy, vibrational modes of adsorbed surface molecules is discussed.