Electronic excitation in a syn-tetrasilane: 1,1,2,2,3,3, 4,4-octamethyltetrasilacyclopentane

Abstract

We present a multistate complete active space second-order perturbation theory (MS-CASPT2) study of the low-lying valence excited states of a peralkylated tetrasilacyclopentane, c-(CH2Si4Me8) (1). The lowest-lying calculated valence excited states are located in the 37,400–50,500 cm−1 region, in perfect agreement with experimental observations, 38,600–50,000 cm−1. The MS-CASPT2 results provide a very good description of the nature, intensity, and position of the observed absorption bands, including the recently detected fourth electronic transition. The computational results have been used as a benchmark for evaluating a time-dependent density functional theory (TD-DFT) procedure suitable for calculations on longer oligosilanes.