TRANSIENT NEGATIVE-IONS IN THE SPECTROSCOPY AND DYNAMICS OF MOLECULES ON SURFACES ORIENTATIONAL EFFECTS

We discuss the role of short-lived molecular negative ions in a variety of surface spectroscopies and dynamical processes occurring on surfaces. Results obtained from electron scattering experiments with physisorbed O2 and CO monolayers on graphite show the important role of molecular orientation in the cross-section for creating a transient negative ion. In the case of O2, two different negative ions states with orthogonal symmetries can be selectively populated by orienting the molecule in two different alignments on the graphite surface. Distinctive, anisotropic cross-sections are also seen in the case of CO. The implications of these spectroscopic results for the dynamical processes are addressed.