ROTATIONAL DISTRIBUTIONS OF EXCITED CN MOLECULES FOLLOWING ELECTRON-STIMULATED AND PHOTON-STIMULATED DESORPTION FROM SURFACES

We report systematic experimental studies of rotational distributions of excited CN desorbed from alkali-metal and alkali-metal-halide surfaces following excitation by incident photons and electrons. Newly measured rotational spectra are found to exhibit temperature-independent non-Boltzmann features that are uniquely correlated to the particular alkali-metal component of the substrate. In addition, we observe that photon-excitation functions and cross sections for CN* desorption also depend strongly on the alkali-metal component of the substrate. The data reveal that rotational distributions arising from electron-stimulated desorption (ESD) and photon-stimulated desorption (PSD) are markedly different from those seen in thermal desorption and molecule-surface scattering. The marked substrate dependence of the rotational distributions indicates that molecular-rotation distributions following ESD and PSD are determined by direct electronic bond breaking and reflect the nature of the potential-energy surfaces that characterize CN-alkali-metal interactions. Utilizing the measured rotational distributions in conjunction with a hindered rotor model, we have constructed angular-dependent potential surfaces.