State-selective energy and angular resolved detection of neutral species ejected from keV ion bombarded C6H6/Ag{111}

We investigated the desorption of neutral benzene (C6H6) molecules and silv er atoms from C6H6/Ag{1 1 1} upon bombardment by 8 keV Ar+ ions. Using stat e-selective resonant ionization spectroscopy, substrate atoms sputtered in the ground and a high-lying metastable state, and ground-state and vibratio nally excited molecules could be probed separately. The silver atom yield, kinetic energy and polar angle distributions were found to be modified upon benzene dosing. From these results, it was inferred that a large fraction of the metastable silver atoms de-excite during collisions with adsorbates. Also the ejection of benzene molecules depends strongly both on the intern al energy of the molecules and the degree of coverage of the Ag surface. Up to monolayer thickness, the benzene molecules are mainly ejected during co llisions with departing substrate particles. Molecules with higher internal energy leave the surface with a distribution shifted towards higher kineti c energies. At multi-layer coverages, a slow desorption mechanism becomes d ominant. It is suggested that only benzene molecules vibrationally excited near the benzene-vacuum interface can survive the ejection process without de-excitation. (C) 2000 Elsevier Science B.V. All rights reserved.