Negative-Ion Photodetachment Studies of Small Silicon and Carbon Clusters

Abstract

Listen

Translate article

This chapter discusses negative-ion photodetachment studies of small silicon and carbon clusters. For small silicon and carbon clusters, photodetachment experiments are a good means of obtaining a detailed picture of the low-lying electronic states of both the neutral and anionic structures. Two forms of negative-ion photodetachment spectroscopy are fixed-frequency photoelectron spectroscopy and threshold photodetachment spectroscopy. In a typical experiment, a mass-selected beam of negative cluster ions undergoes photodetachment by laser irradiation. The generated photoelectrons are subsequently energy analyzed, thereby yielding information about the electronic and vibrational states of the neutral. Negative-ion photodetachment is a very powerful spectroscopic probe for clusters, because one can readily mass-select the species of interest prior to spectroscopic interrogation, thus eliminating any uncertainty surrounding the nature of the signal carrier. Furthermore, the selection rules for photodetachment are different from those of optical spectroscopy, thus allowing one to probe electronic states that are dark (forbidden) in absorption or emission experiments. The two photodetachment techniques differ in their electron energy analysis scheme. Although the energy resolution of the threshold photodetachment spectrometer is substantially higher than that of the photoelectron spectrometer, it is the combination of the results from the two instruments that yields the complete picture.