Photoelectron spectroscopy of silicon–fluorine binary cluster anions (SinF−m)

Electronic properties of silicon–fluorine cluster anions (SinF−m; 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 F2 gas. The highly abundant clusters are SiF−m (m=3 and 5) and SinF− (n=6, 7, and 10) in their mass spectra. In the photoelectron spectra of SiF−m (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 Sin 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.