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 → σ*(ND) transition at both grazing and normal photon incidence angles and its enhanced yield shows no polarization dependence despite of direct PSID, which indicates the ND 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.