Tracking the motion of chemisorbed molecules on their adsorption sites.

A new method, the time of flight-electron-stimulated desorption ion angular distribution method (TOF-ESDIAD), is described. The method permits the mapping of the lateral momentum distribution of adsorbed species on their adsorption sites. Examples of the study of the rotation of chemisorbed PF3 molecules and the frustrated lateral translation of chemisorbed CO molecules, both on single-crystal metal surfaces, are given. The observed anisotropy of the frustrated translation of CO is postulated to occur as a result of the 2pi* orbital alignment in chemisorbed CO along the close packed direction of the Cu(110) substrate.