  We studied quantitatively the photochemistry of solid O3 and O2 films at 193
nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure
ozone destroyed O3, but a small amount of ozone remained in the film at high
fluence. Photolysis of pure O2 produced O3 in an amount that increased with
photon fluence to a stationary level. For both O2 and O3 films, the O3:O2 ratio
at saturation is 0.03, nearly 10-30 times larger than those obtained in gas
phase photolysis. This enhancement is attributed to the increased
photodissociation of O2 due to photoabsorption by O2 dimers, a process
significant at solid state densities. We obtain initial quantum yield for ozone
synthesis from solid oxygen, {\Phi} (O3) = 0.18 and for destruction of ozone
and oxygen in their parent solids, {\Phi} (- O3) = 1.7 and {\Phi} (-O2) = 0.28.
Combined with known photoabsorption cross sections, we estimate probabilities
for germinate recombination of 0.15 for O3 fragments and 0.90 for oxygen atoms
from O2 dissociation. Using a two-parameter kinetic model, we deduce the
average probabilities for the reaction of an O atom with O2 and O3 to be 0.10
and 1, respectively. These probabilities are the same for both O2 and O3 films,
even though the distribution of kinetic and internal energy of the
photofragments is very different in both cases. This finding suggests efficient
energy relaxation of photofragments in the solid occur prior to their reactions
with other species.
