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 surfa ces following excitation by incident photons and electrons. Newly meas ured rotational spectra are found to exhibit temperature-independent n on-Boltzmann features that are uniquely correlated to the particular a lkali-metal component of the substrate. In addition, we observe that p hoton-excitation functions and cross sections for CN desorption also depend strongly on the alkali-metal component of the substrate. The da ta reveal that rotational distributions arising from electron-stimulat ed desorption (ESD) and photon-stimulated desorption (PSD) are markedl y different from those seen in thermal desorption and molecule-surface scattering. The marked substrate dependence of the rotational distrib utions indicates that molecular-rotation distributions following ESD a nd PSD are determined by direct electronic bond breaking and reflect t he nature of the potential-energy surfaces that characterize CN-alkali -metal interactions. Utilizing the measured rotational distributions i n conjunction with a hindered rotor model, we have constructed angular -dependent potential surfaces.