MODELING SPIN-ORBIT COUPLING IN THE HALOCARBENES

Halocarbenes are organic reactive intermediates with a neutral divalent carbon atom that is covalently bonded with a halogen and another substituent. Being the smallest carbenes that exhibit closed shell ground states, they have contributed greatly to our understanding of the reactivity of singlet carbene species and the factors that contribute to singlet-triplet energy gaps. We report an analysis of spin-orbit coupling in the mono-halocarbenes, CH(D)X, where X = Cl, Br, I. Single Vibronic Level (SVL) emission spectroscopy and Stimulated Emission Pumping (SEP) spectroscopy have been used to probe the ground vibrational level structures in these carbenes which have indicated the presence of perturbations involving the low-lying triplet state. In this talk, we present two approaches to model these interactions. Anharmonic constants, singlet-triplet gaps and geometry-dependent spin-orbit (SO) coupling surfaces were computed using high-level explicitly correlated methods such as CCSD(T)-F12b and MRCI-F12. These were used to evaluate SO coupling matrix elements and hence predict/fit mixed-perturbed singlet-triplet experimental levels. Results are also compared to those from a simpler model using a geometry-independent SO-constant