The kinetics of adsorption and thermal desorption of NO on stepped Pt single crystal surfaces

Abstract

The kinetics of adsorption and thermal desorption of nitric oxide on Pt field emitter surfaces has been studied by means of pulsed field desorption mass spectrometry (PFDMS). Adsorption on the high index planes with terraces of (111) orientation occurs molecularly with high initial sticking probabilities S=0.65,...,0.9. By varying the repetition frequency of the desorbing field pulses, i.e., by varying the field free reaction time tR (100 μs to 1 s), the mean lifetimes before thermal desorption of the NOad have been measured. The temperature dependence of the mean lifetimes has been evaluated. An activation energy of 139 kJ/mol and a preexponential of 3.8×10−15 s are found. These rate parameters are dominated by adsorption at step sites as verified on the basis of a model comprising multiple state adsorption and desorption. Dissociation of NOad has not been observed on stepped Pt(111), but has been on stepped Pt(100).