UC Irvine

Atomic oxygen is photogenerated in solid D-2 by 193 nm irradiation of samples initially doped with molecular oxygen. The atoms are detected by laser-induced fluorescence at the O(S-1 --> D-1) transition, which occurs at 559 nm, with a fluorescence lifetime of 230 mus. The absorption leading to this emission is indirect, attributed to O-2(X):O(P-3) pairs. Complementary studies are carried in solid D-2 co-doped with Xe and O-2, in which, in addition to ionic XeO centers, the atomic O(S-1 --> D-1) transition with a radiative lifetime of 50 mus is observed. The photogeneration of the atomic centers and the stability of the atomic and molecular emissions are sensitive to sample preparation and thermal and irradiation histories. In annealed solids at temperatures below 6.5 K the atomic emission does not bleach, implying that the vertically prepared O(D-1) atoms undergo intersystem crossing to form O(P-3) rather than react with D-2. The barrier to insertion on the O(D-1)+D-2 potential energy surface in solid D-2 is explained as a many-body polarization effect. The recombination of O(P-3) atoms can be initiated thermally and can be monitored by their thermoluminescence at the molecular O-2(A'-->X) transition. The thermal onset of recombination varies between 5.5 K and 9 K, depending on the sample preparation method. In all cases, the thermally induced recombination is catastrophic, accompanied by thermal runaway, pressure burst, and material loss. This is interpreted as an indication that the process is initiated by self-diffusion of the host, consistent with the notion that atomic O centers stabilize the host lattice. (C) 2000 American Institute of Physics. [S1063- 777X(00)00709-X].