Peralkylated Tetrasilanes: Conformational Dependence of the Photoelectron Spectrum

Abstract

Photoelectron spectra of conformationally constrained methylated tetrasilanes 1−5 were measured, extending to the full 0−180 ° range the previously available 0−80° region of SiSiSiSi dihedral angles ω provided by the monocyclic analogues 6−9. The resulting complete picture of the conformational dependence of photoionization of the n-tetrasilane moiety is unfortunately somewhat distorted by differential polarizability effects of the alkyl chains used for conformational constraint. The lowest three ionization potentials are attributed to σSiSi bonding orbitals. The first and the third of these decrease a little as ω goes from 0 to 180°, whereas the second one increases distinctly. Within the framework of the Koopmans' approximation, these trends in backbone MO energies agree with those computed in the HF/TZ//MP2/TZ approximation and those obtained from the simple Hückel ladder C model.