Auger-final-state selected ion desorption study of condensed NH3 and ND3 by using Auger electron-photoion coincidence spectroscopy

Photostimulated ion desorption induced by core-level excitations was studied for condensed NH3 and ND3 by using Auger electron-photoion coincidence (AEPICO) spectroscopy with synchrotron radiation. Series of AEPICO spectra for condensed NH3 and ND3 were measured as a function of the electron kinetic energy around the N KVV Auger electron energy range. AEPICO yields of both H+ and D+ were enhanced at the electron kinetic energies corresponding to the N KVV Auger transitions, which provide clear evidence of an Auger-stimulated ion desorption mechanism. We analyzed the fine structure of the AEPICO yield spectra on the basis of the assignment of Auger final states, and suggested that Auger final states containing two holes in the same valence orbital efficiently lead to ion desorption. The AEPICO yield of D+ was found to be one-third to one-half the yield of H+. We concluded that the isotope effect is derived from the reneutralization and recapture of Dc on the surface because of the slow desorption velocity of D+ compared with that of H+.