Laser spectroscopic detection of OH in catalytic reactions on platinum

We are presently investigating the emission of OH radicals by laser-induced fluorescence (LIF) in the H2 + 1/202 → H2O reaction on polycrystalline platinum. Results are obtained for emission yields of OH as functions of pressure (5-500 mTorr), temperature (950-1300 K), and O2/H2 ratios. The rotational temperature distribution of the desorbing OH molecules is determined, showing a significant dependence of the total pressure. The rotational temperature is only 50-75% of the surface temperature of the catalyst, i.e., the emitted OH radicals are not in thermal equilibrium when they are produced. Apparent desorption energies are also achieved. They vary from 30 to 60 kcal/mole for different O2/H2 ratios.