6533b853fe1ef96bd12abf7a

RESEARCH PRODUCT

Multiconfigurational second-order perturbation calculation of the electronic absorption spectrum of trisilane, Si3H8

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The low-lying singlet excited states of trisilane have been computed using the complete active space self-consistent field (CASSCF) method, second-order perturbation theory (CASPT2), and the extended multistate CASPT2 (MS-CASPT2) approach, and a generally contracted basis set of atomic natural orbitals (ANOs) including Rydberg functions. The ground state structure was obtained from an ab initio optimization at the second-order M⊘ller-Plesset perturbation theory (MP2) level using Dunning's correlation-consistent triple-zeta basis set (cc-pVTZ) and agrees well with experiment. The calculation of the electronic transitions included the lower valence excited states and two Rydberg series converging to the first two ionization potentials. Only the MS-CASPT2 method gave an accurate description of the observed electronic excitations since it provided an effective separation of the valence and Rydberg states. In contrast with previous assignments, three states of valence character were found below the first Rydbe...