Study of ion desorption induced by a resonant core-level excitation of condensed NH 3 using Auger-electron photo-ion coincidence (AEPICO) spectroscopy combined with synchrotron radiation

Photostimulated ion desorption at the 4a ₁ ← N 1s resonant transition of condensed NH ₃ 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 hν = 399 eV which is ascribed to the resonant transition from the N 1s to the NH antibonding 4a ₁ orbital. The electron emission spectrum at the 4a ₁ ← N 1s 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 1s 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 1s resonance is concluded to originate from the spectator-Auger transitions and from the normal-Auger transitions following the delocalization of the excited electron.