Time-dependent chemiluminescence from the surface-catalysed recombination of O and NO on polycrystalline platinum

Abstract

The chemiluminescence produced by the surface-catalysed recombination of nitric oxide with a supersonic beam of atomic oxygen on polycrystalline platinum has been studied. The dependence of the luminescence on time, substrate temperature, O and NO fluxes and pre-exposure to the O-atom beam has been investigated. An initial luminescent signal was observed which decayed with time to a steady state. The initial luminescent intensity at any given temperature was less than the signal observed previously on a nickel sample, and it is suggested that this arises from the different adsorption characteristics of NO, O₂ and electronically excited NO₂ on the two surfaces. Also apparent was a ‘fast’ decay in the luminescence for temperatures at or below 220 K, which lasts for only a few seconds before the reaction proceeds by a slower decay process. This fast decay, which was not detected on nickel, may arise from the initial reaction of chemisorbed O atoms on the oxidised platinum surface with NO. The mechanism proposed previously has been used to determine the rate constants of the reaction.