Dynamics of dissociative attachment reactions in electron stimulated desorption: Cl− from condensed Cl2

Energy analysis of Cl− ions produced by dissociative attachment in electron stimulated desorption from Cl2 condensed on a platinum substrate is reported. The electron energy dependence of the Cl− signal exhibits two peaks around 2 and 5 eV which arise, respectively, from the 2Πg and 2Πu core-excited Cl−*2 resonant states. At higher Cl2 coverages, a third peak is observed around 11.5 eV. From kinetic energy distributions, it is possible to ascribe this latter peak to Cl− ions formed via the 2Πu resonance by electrons which have suffered energy losses through the excitation of low-lying electronic states of molecular chlorine. In the energy range of the 2Πu Cl−*2 resonance, we observe that multiple scattering processes are also important and that the curve representing the kinetic energy of Cl− ions formed via a single scattering process as a function of incident electron energy is a straight line with a slope 1/2. This indicates that the chlorine lattice is not involved in the dissociation dynamics.