Role of excitons in electron- and photon-stimulated desorption of neutrals from alkali halides

Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields (IP3/2)-P-2 and P-2(1/2) with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the Gamma (3/2)-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 With hyperthermal velocity and is in competition with self-trapping. Spin memory of the Gamma -exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides