a b s t r a c tEfficient production of H atoms, O atoms and OH radicals was confirmed by laser spectroscopic measurements in the catalytic decomposition of H 2 , O 2 and their mixtures on a heated Ir filament. No change in electric resistivity was observed when the filament was kept at 2350 K in the presence of 1.0 Pa of pure O 2 , showing that oxidation is minor. Arrhenius-type temperature dependences were observed for the densities of H (O) atoms in pure H 2 (O 2 ) systems. In the H 2 /O 2 mixed system, the H-atom density was almost independent of the O 2 partial pressure, although the O-atom and OH-radical densities increased with the O 2 pressure. These O 2 pressure dependences are completely different from those observed for W. Ir is less poisoned by O 2 compared to W. In addition, direct production of H 2 O molecules on Ir surfaces must take place besides the production of radical species.

Production of O atoms was confirmed in the catalytic decomposition of O 2 , NO, N 2 O and NO 2 on a heated Ir filament. No change in electric resistivity was observed when the filament was kept at 2350 K in the presence of 0.8 Pa of these species, showing that oxidation is not taking place under such conditions. The O-atom densities were evaluated by a vacuum-ultraviolet laser-induced fluorescence technique at 130.2 nm as well as a vacuum-ultraviolet laser absorption technique, by which the absolute values can be evaluated. Arrhenius-type filament temperature dependences were observed for the O-atom densities in all systems. The activation energies for nitrogen oxides were similar, but that for O 2 was smaller. The O-atom density was the highest when O 2 was used as a source gas and the density could be increased up to 2 × 10 12 cm-3. The O-atom density increased with the oxidant pressures, but showed saturation. The possible causes of such behaviors are discussed on the basis of the changes in the coverage conditions of the catalyst surfaces.

Production of O atoms, H(D) atoms, and OH(OD) radicals was confirmed in the catalytic decomposition of H 2 O(D 2 O) on a heated Ir filament by laser spectroscopic techniques, such as vacuum-ultraviolet laser-induced fluorescence. The highest steady-state OH density achieved was 2 10 11 cm -3 . The filament temperature dependences of the radical densities were not Arrhenius-type, in contrast to the results on the decomposition of H 2 and O 2 . 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.

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4,8,10-Trithiadibenzo[cd,ij]azulene 8-oxides were prepared and their photolysis provided a convenient procedure to yield the corresponding aldehydes and ketones together with 4,8,9-trithiacyclopenta[def]phenanthrene.