The exoemission in the reaction of O-2 with Cs surfaces is found to de
pend strongly on the translational energy of the impinging O-2 molecul
es. Seeded beam experiments show that in the initial oxidation state e
xoemission increases with increasing O-2 velocity. Above 0.5 eV of kin
etic energy the increase is found to be proportional to exp(-v/v) wit
h a value v of 1.6 x 10(4) m/s.