Photoelectron spectroscopy of iron–sulfur cluster anions

Iron–sulfur cluster anions (FenS−m, n=1–6, m=1–6) have been studied using photoelectron spectroscopy (PES) with a magnetic-bottle-type time-of-flight electron spectrometer. The FenS−m cluster anions were formed in a laser vaporization cluster source. It was found that the stable cluster ions are the ones with compositions of n=m and n=m±1. The electron affinities were measured from the onsets of the PES spectra. Three low-lying electronic states were observed for FeS. The PES spectra of FenS− (n=1–4) series show a unique similarity, indicating that the Fe atom addition to FeS− has little effect on the electronic property of FeS. The PES spectra of FenS−2 series show a similarity among the cluster anions with n=2–4, showing that Fe2S−2 is the structural framework of these clusters. For FenS−3 series, Fe3S−3 is proposed to be the structural framework. The electronic properties and geometrical structures of the clusters are discussed.