15min:

LU XU, D. E. WOON AND T. H. DUNNING JR., Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

High level MRCI and RCCSD(T) calculations using triple and quadruple zeta quality correlation consistent basis sets were used to study the low-lying singlet and triplet states of CH₂, CF₂, and CHF. The bonding in carbon was found to be very similar to that of sulfur, where there is also a competition between states that form through normal covalent bonding and recoupled pair bonding. The recoupled pair bonding model was used to investigate these states systematically to see how closely they resemble the behavior of SF₂, which has a ¹A₁ ground state and ³B₁ and ³A₂ excited states. In addition to accounting for the separations and ordering of the lowest singlet and triplet states of each species, the less-studied ³A₂ states of CH₂ and CF₂ and the ³A'' state of CHF were investigated and compared to gain insight into the underlying reasons for the energetic and bonding differences between these species. Interestingly, the ³A₂ state of CH₂ is a cyclic structure, the ³A₂ state of CF₂ is bent but not cyclic (resembling the same state of SF₂), and the analogous minimum structure on the ³A'' surface of CHF is a C---HF complex.