Study of ion desorption induced by a resonant core-level excitation of condensed NH3 using Auger-electron photo-ion coincidence (AEPICO) spectroscopy combined with synchrotron radiation

Photostimulated ion desorption at the 4a(1)<--N Is resonant transition of condensed NH3 was studied using electron emission spectroscopy and Auger-electron photoion coincidence (AEPICO) spectroscopy. The total ion yield divided by the Auger-electron yield exhibited a threshold peak at hv=399 eV which is ascribed to the resonant transition from the N Is to the N-H antibonding 4a(1) orbital. The electron emission spectrum al the 4a(1)<--N Is resonance is decomposed into three components: a valence photoelectron emission spectrum, and normal-and resonant-Auger-electron emission spectra. We ascribe the resonant-Auger-electron emission spectrum mainly to spectator-Auger transitions on the basis of the peak assignment. A series of AEPICO spectra at the 4a(1)<--N Is resonance was also measured as a function of the Auger-electron kinetic energy. The electron kinetic energy dependence of the H+ AEPICO yield displays a shape approximately similar to that of the mixed spectrum of normal-and spectator-Auger-electron emission spectra. Based on this result the H+ desorption at the 4a(1)<--N Is resonance is concluded to originate from the spectator-Auger transitions and from the normal-Auger transitions following the delocalization of the excited electron. (C) 1997 Elsevier Science B.V.