LASER-INDUCED FLUORESCENCE STUDIES OF ROTATIONAL STATE POPULATIONS OF OH DESORBED IN THE OXIDATION OF HYDROGEN ON PT

The state-sensitive laser-induced fluorescence technique has been employed to study the rotational state population of OH radicals desorbed from a polycrystalline platinum foil in the H2 + 1 2O2 → H2O reaction. The experiments were performed at steady-state reaction conditions in the pressure (p) range 2-200 mTorr at a catalyst temperature of T = 1200 K. In the limit p → 0 Boltzmann-type plots produce almost straight lines with a rotational temperature Trot T = 0.81 ± 0.03onstrating the rotationa cooling upon desorption previously observed by Hsu and Lin [J. Chem. Phys. 88 (1988) 432]. The rotational cooling is smaller for OD. For both molecules these results are compatible with desorption of thermally equilibrated molecules (on the surface), which loose one rotational quantum upon desorption. At higher pressures significant deviations from Boltzmann distributions and rotational cooling is observed due to gas-phase collisional processes. © 1990.