Rotational energy accommodation in OH radicals desorbing from a polycrystalline Pt foil and a Pt(111) single crystal

Abstract

Boltzmann-like rotational energy distributions were obtained for desorbing OH radials formed in the oxidation of hydrogen on a Pt(111) single crystal and polycrystalline Pt foil by using the laser-induced fluorescence method in conjunction with an UHV apparatus. For an O/H=1 reactant gas mixture, relatively high rotational energy accommodation was indicated by the rotational to surface temperature ratios Tr/Ts of 0.85±0.03 over the temperature range 1227–1479 K for the Pt(111) single crystal, and of 0.86±0.04 over 1283–1475 K for the polycrystalline Pt foil. Tr seemed to be proportional to Ts over these temperature ranges. The lack of noticeable dependence of Tr/Ts on the O/H reactant gas mixture ratio suggests that the rotational energy accommodation is not sensitive to the apparent Pt–OH bond strength.