Spectroscopic studies of collision-induced desorption from surfaces

It is now possible to perform spectroscopic studies of particles desorbed from surfaces by energetic collisions. In this discussion, experiments are described which allow measurement of the energy and angle of ejection of atoms in specific electronic states. The states are detected by directing a pulsed laser beam over the sample surface and ionizing the desorbing atom via multiphoton resonance absorption. The results are then compared to molecular dynamics computer simulations of the ion-bombardment event. For this set of calculations, a special extension of the classical model has been developed which allows the influence of electronic excitation to be included. There is excellent agreement between theory and experiment when the ₄F_7/2 and ⁴F_9/2 states of Rh{100} are examined. The dependence of excitation probability on velocity and angle suggests that a fraction of the ejected atoms are excited via collisions 1-20 Å above the surface and that these atoms make a significant contribution to the excited atom yield at low velocities. In general, these types of studies are providing a detailed understanding of the very complex ion/solid interaction event.