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RESEARCH PRODUCT

The Transoid, Ortho, and Gauche Conformers of Decamethyl-n-tetrasilane, n-Si4Me10:  Electronic Transitions in the Multistate Complete Active Space Second-Order Perturbation Theory Description

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Multistate complete active space second-order perturbation theory (MS-CASPT2) is used to improve earlier descriptions of the low-energy valence excited states of the transoid, ortho, and gauche conformers of decamethyl-n-tetrasilane, n-Si4Me10, using a generally contracted basis set of atomic natural orbitals (ANOs) at a ground-state geometry optimized in the second-order Moller−Plesset perturbation theory (MP2) approximation with Dunning's correlation consistent triple-ζ basis set (cc-pVTZ) on the silicon atoms and the 6-31G* and 6-31G basis sets on the carbon and hydrogen atoms, respectively. Relative energies, relative free energies, and mole fractions of the transoid, ortho, and gauche conformers are reported at various temperatures. CASPT2 ionization potentials for the three conformers are calculated and found to agree with photoelectron spectra. The first eight valence excited states of each conformer are computed and analyzed in terms of natural orbitals. Most of the important excitations are due t...