Chemisorptive exoemission induced by vibrationally excited N2O molecules

The energy distributions and the kinetics of the electron emission as well as the kinetics of Na abstraction have been measured during the scattering of vibronically excited N2O molecules on Cs films. The chemisorption of cold N2O molecules leads to a low-energy electron emission which proceeds in two characteristic stages. Whereas the short-term initial chemisorption is characterized by moderate electron emission, the late reaction stage exhibits durable and more efficient exoactivity. The chemisorption of hot N2O molecules inverts this intensity ratio. It raises the intensity of the initial exoemission by more than 1 order of magnitude. Within the late reaction stage, the emission is only slightly affected by the vibronic excitation of the chemisorbing molecules. The pronounced enhancement of the initial emission, I-init, strongly depends on the mean temperature of the N2O beam, T*. The observed relation, I-init(T*), can be explained when considering two contributions: The increased probability for dissociation of N2O molecules in the excited bending vibronic mode is due to the long-distance harpooning. The second one originates from ground state molecules which dissociate only when the short-distance interaction with Cs atoms leads to the formation of a Cs+aO-b bond. By comparison of the efficiency of the Nz abstraction with the yield for exoemission, a nondissociative channel for electron emission becomes evident. For Cs layers characterized by low work function values around 1.65 eV, molecules in the stretching vibrational mode also participate in the observed emission.