Photoelectron spectroscopy of silicon-fluorine binary cluster anions (SinFm-)

Electronic properties of silicon-fluorine cluster anions (SinFm-; n=1-11, m=1-3) were investigated by photoelectron spectroscopy using a magnetic-bottle type electron spectrometer. The binary cluster anions were generated by a laser vaporization of a silicon rod in an He carrier gas mixed with a small amount of SiF4 or F-2 gas. The highly abundant clusters are SiFm- (m=3 and 5) and SinF- (n = 6, 7, and 10) in their mass spectra. In the photoelectron spectra of SiFm- (m = 1-5), the clusters having odd m have higher electron affinity (EA) than those having even m, indicating that the even/odd alternation in EA is attributed to their electronic structures of a closed/open valence shell. Comparison between photoelectron spectra of SinF- and Si-n(-) (n=4-11) gives the insight that the doped F atom can remove one electron from the corresponding Si-n(-) cluster without any serious rearrangement of Si-n framework, because only the first peak of Si-n(-), corresponding singly occupied molecular orbital (SOMO), disappears and other successive spectral features are unchanged with the F atom doping. In some clusters, furthermore, the vibrational structures could be resolved to determine a vibrational frequency and to presume the geometry with ab initio molecular orbital calculations. (C) 1996 American Institute of Physics.