Direct and indirect processes in photon-stimulated ion desorption from condensed formamide

A preliminary investigation of photon-stimulated ion desorption (PSID) from condensed deuterated formamide (HCOND2) by using polarization-angle-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with velocity-selected time-of-flight (TOF) mass spectrometry, is presented. It was found that the PSID yield of total D+ ion is enhanced by the N 1s -> sigma*(N-D) transition at both grazing and normal photon incidence angles and its enhanced yield shows no polarization dependence despite of direct PSID, which indicates the N-D bonds are not aligned with the surface-oriented CNO molecular plane of HCOND2. It was also found that the fastest velocity components of H+ and D+ ions monotonically decrease as the energy at the normal incidence angle. This finding suggests that X-ray-induced electron stimulated desorption (XESD) via secondary electrons resulting from valence photoelectrons; indirect PSID is a dominant process in the fastest components. (c) 2005 Elsevier B.V. All rights reserved.