Electronic excitation in a saturated chain: an MS-CASPT2 treatment of the anti conformer of n-tetrasilane

The singlet-singlet electronic spectrum of the anti conformer of n-tetrasilane is studied using multiconfigurational wave functions (CASSCF), second-order perturbation theory (CASPT2), and its multi-state extension (MS-CASPT2) in conjunction with large ANO-type basis sets including Rydberg functions. The results are consistent with the available experimental data and are easily understood in terms of a simple Huckel model of sigma-delocalization.