Catalytic Decomposition of HO(DO) on a Heated Ir Filament to Produce O and OH(OD) Radicals

ABSTRACT

Production of O atoms, H(D) atoms, and OH(OD) radicals was confirmed in the catalytic decomposition of H₂O(D₂O) on a heated Ir filament by laser spectroscopic techniques, such as vacuum-ultraviolet laser-induced fluorescence. The highest steady-state OH density achieved was 2x10¹¹ cm^-3. The filament temperature dependences of the radical densities were not Arrhenius-type, in contrast to the results on the decomposition of H₂ and O₂. Especially, OH(OD) density decreased with the increase in the filament temperature over 2100 K. The decomposition process changes from the production of H+OH(D+OD) to that of ₂H+O(₂D+O) with the increase in the catalysis temperature. This change in the exit channel could not be reproduced by model calculations using the CHEMKIN software package when Arrhenius-type temperature dependences were assumed for the elementary-step rate constants on surfaces. It is necessary to assume that the desorption energy of OH(OD) is surface coverage dependent.