The reaction of O-2 With Li and Cs films is accompanied by the emission of electrons. The variations of the initial yields with the velocity of the impinging molecules is exploited to access the dynamics of the adsorption process. The data are analysed in terms of a model where chemisorption proceeds via an intermediate O-2(2-) species. This O-2(2-) state readily dissociates while the de-excitation of the resulting O- into O2- may cause electron emission. From a comparison with experimentally observed electron yields the reaction time and velocity uptake of the products is accessed.
