Ultrafast H+ desorption from an isolated NH3 monolayer adsorbed on a Xe film induced by a resonant core electron transition studied by Auger electron-photoion coincidence spectroscopy

Mechanism of ion desorption from an isolated NH3 monolayer adsorbed on a Xe film (NH3/Xe) induced by a resonant core electron excitation is studied us ing Auger electron-photoion coincidence (AEPICO) spectroscopy. The total io n yield spectrum of NH3/Xe exhibits a threshold peak at the resonant excita tion from N 1s to the 4a(1) N-H antibonding orbital. The Auger electron spe ctrum of the isolated NH3 at the 4a(1) <-- N 1s resonant transition is foun d to be mainly due to spectator-Auger transitions. A series of AEPICO spect ra at the 4a(1) <-- N 1s resonance is measured for the electron kinetic ene rgies corresponding to the spectator Auger transitions. The AEPICO spectra show that H+ is the only desorbed ion species. The electron kinetic energy dependence of the H+ AEPICO yield displays a structure similar to that of t he spectator-Auger electron spectrum. This result indicates that the H+ des orption probabilities are independent of the final states of spectator-Auge r transitions. Based on these results, we suggest that the repulsive potent ial surface of the (N 1s)(-1)(4a(1))(1) state is responsible for the H+ des orption, that is, ultrafast H+ desorption mechanism is favorable in this sy stem.