PHOTO-STATIONARY STATE OF UV PUMPED MATRIX-ISOLATED O-2

The 193 nm excitation of O-2 in crystalline Ar and Kr leads to a photo-stationary state, whereby approximate to 50% of the population is transferred from O-2(X(3) Sigma(g)(-)) to a((1) Delta(g)). A kinetic analysis yields absorption cross sections of approximate to 10(-21) cm(2), from X and a states, and establishes the final states as A'((3) Delta(u)) and the repulsive (1) Pi surface, respectively. The A'<--X transition is enhanced approximate to 3 orders of magnitude in the solid, by borrowing intensity from the (3) Pi <-- X transition. Only molecules isolated at defect sites, undergo permanent dissociation. Substitutionally isolated O-2 does not dissociate at excess energies less than or equal to 2.5 eV.