Low-energy 5–100 eV/electron- and ultraviolet 6.4 eV/ photon-stimulated desorption of neutral fragments from NaNO3 single crystals

The low-energy 5–100 eV.electron-stimulated desorption ESD. of neutrals from NaNO3 single crystals is compared with 193 nm 6.4 eV.photon-stimulated desorption PSD.. The major ESD and PSD products, NO 2P., and O 3P., were detected via laser resonance enhanced multiphoton ionization. The less abundant NO2and O2 products were detected only via quadrupole mass spectrometry. The ESD yields of NO 2P.and O 3P. show a linear dependence upon incident electron-beam current, indicating single-electron desorption events. The PSD yields of these fragments show a 1-photon dependence on laser fluence, with no observable threshold down to 1 mJrcm2. For both ESD and PSD, the velocity distributions of NO 2P.and O 3P. have non-thermal components, consistent with near-surface dissociation events. We propose a mechanism for NO 2P.and O 3P. desorption which involves exciton production, localization and decay at the vacuum-surface interface. The NO2and O2velocity distributions are equilibrated to the 423 K surface temperature and the formation of these products may involve reactive scattering of O-atoms. Since the neutral product yields and energy distributions are very similar for ESD and PSD, the final states involved in desorption must be similar. q1998 Pacific Northwest National Laboratory. Published by Elsevier Science B.V.