Mass distribution of sulfide cluster ions, X nS m± (XC, Si, Ge)

Abstract

A series of binary cluster ions composed of sulfur and group IVA elements, X n S m ± (XC, Si, Ge), were generated by direct laser vaporization. Their mass distribution was recorded by a time-of-flight mass spectrometer. The relative abundance of most carbon-sulfur and silicon-sulfur cluster ions can be described by the statistical distribution rule. The carbon-sulfur cluster ions containing a single sulfur atom have a strong affinity for trapping an extra hydrogen atom and their signal intensity exhibits a dramatic even/odd alternation. Parity of the alternation effect depends on the positive or negative charge carried by the cluster ions. The cluster ions containing two sulfur atoms show higher signal intensity and their alternation effect is not affected by the polarity. Most silicon-sulfur cluster anions can be described by two log-normal curves. One series of cluster ions can be represented as (Si 2S 8)(SiS 2) n −, and the other as (Si 2S 7)(SiS 2) −. Both series of cluster ions take SiS 2 as the growing unit. Analysis of the mass distribution suggests that both carbon-sulfur and silicon-sulfur cluster ions adopt a low-dimensional geometry. However, for the former, sulfur atoms are located at the end of the C-C chain; for the latter, sulfur atoms bridge the clustering silicon atoms. Germanium and sulfur can only form small cluster anions. The signal intensity of germanium-sulfur cluster anions, Ge n S m −, drops rapidly with the increase in n. Generally, the bonding nature of the cluster ions X n S m ± changes from covalent to ionic as X changes from carbon to germanium.