Molecular Beam Study of the Oxidation of Deuterium on a (111) Platinum Surface

Abstract

The reaction ${\mathrm{D}}_2+\frac{1}{2}{\mathrm{O}}_2\to {\mathrm{D}}_2\mathrm{O}$ occurring on a (111) Pt surface has been investigated using modulated molecular beam techniques. With a molecular beam of D₂ and a (111) Pt surface immersed in an O₂ ambient, the production of D₂O was studied as a function of D₂ flux and temperature, O₂ pressure, Pt temperature and the angle of incidence of the D₂ beam. From these data the rate of production of D₂O can be expressed by a reaction rate proportional to $$P_{{\mathrm{D}}_2}^{\text{2.0}}{P}_{{\mathrm{O}}_2}^{\text{0.8}}\hspace{0.17em}\exp \text{[−3.6 (}\mathrm{kcal}/\mathrm{mole}{\mathrm{)\; /\; kT}}_{{\mathrm{D}}_2}\mathrm{]\hspace{0.17em}}\exp \text{[−12 (}\mathrm{kcal}/\mathrm{mole}{\mathrm{)\; /\; kT}}_{\mathrm{Pt}}]$$ in the pressure and temperature regime $P_{{\mathrm{D}}_2}{\text{∼ 10}}^{\text{−7}}$ torr, $P_{\mathrm{O}{}_2}{\text{∼ 10}}^{\text{−5}}$ torr, $T_{\mathrm{D}{}_2}\text{∼ 1200°}\mathrm{K}$ , and $T_{\mathrm{Pt}}\text{∼ 700°}\mathrm{K}$ . Further, a reaction mechanism which is consistent with this rate expression and also with the observed angular dependence is presented.