Energy and angular distributions of particles desorbed from surfaces using multiphoton resonance ionization detection

Abstract

Multiphoton resonance excitation has been employed to ionize neutral atoms and molecules desorbed from surfaces bombarded by 5 keV Ar+ ion beams. By positioning a laser beam above the target it is possible to image the ions onto a microchanneiplate detectorand to obtain energy andangle-resolveddistributions. These distributions maybecompared directly to classical dynamics computer simulations ofthe ion/impact event. Results are presented using the (001), (1 1 1) and (331 crystal faces ofRh to illustrate how the distributions contain specific structural information. Moreover, we compare the distributions from (1 1 1) to secondary ion angular distributions. This comparison suggests that there are special impact points which lead to ion formation from clean metal surfaces. Finally, we present preliminary measurements for the MPRI of pyrene molecules desorbed from polycrystalline gold surfaces. Theresults suggest this technique may be valuable for monitoring reaction intermediates presentat very low concentration on catalyst surfaces.