Reactivity of ionic silicon clusters with methylsilane studied by Fourier transform ion cyclotron resonance mass spectrometry

The reactivity of Si_1-7⁺ and Si_1-7^- with methylsilane is investigated by Fourier transform ion cyclotron resonance mass spectrometry. Product distributions for Si_1-5⁺ depend strongly on cluster size; no reactions are seen for Si_6-7⁺ and Si_1-7^-. The reaction rates of Si_1-5⁺ decrease with increasing size which is correlated with an increased delocalization of positive charge on the larger clusters. A reaction mechanism is proposed involving the lone pair, singlet coupled electrons on divalent silicon atoms in the clusters. Extra stability of "magic number" clusters has minor effects on their reaction rate and is not reflected in their product spectra.