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.