Rotational energy accommodation and apparent desorption energy of OH formed in the catalytic reaction of NO2 and H2 over Pt(111): Effect of surface oxygen coverage

Abstract

Laser induced fluorescence has been used to study the desorption dynamics of OH radicals produced by the reaction of NO2 and H2 on Pt(111), under ultrahigh vacuum conditions. We measure an apparent Arrhenius activation energy for desorption that increases from 25 to 38 kcal/mol as the NO2 to H2 ratio in the dosing mixture decreases from 2 to 0.05. Boltzmann-like rotational energy distributions with relatively high rotational to surface temperature ratios (Tr/Ts =0.69−0.87) are reported for crystal temperatures between 1078 and 1433 K. We have also observed a small but definite dependence of the Tr/Ts ratio on both Ts and the dosing mixture ratio. These results are compared with earlier data from the O2+H2 reaction over Pt(111) and interpreted in terms of O coverage.