High resolution study of spin-orbit mixing and the singlet-triplet gap in chlorocarbene: Stimulated emission pumping spectroscopy of $CH35Cl$ and $CD35Cl$ Available to Purchase

We report on high resolution studies of spin-orbit mixing and the singlet-triplet gap in a prototypical halocarbene, CHCl, using stimulated emission pumping (SEP) spectroscopy from the $ÃA1″$ state. Results are reported for two isotopomers, $CH35Cl$ and $CD35Cl$⁠. We have obtained rotationally resolved spectra for the majority of $X̃A1′$ levels lying between 0 and $6000cm−1$ above the zero-point level that were previously observed under low resolution in single vibronic level emission studies and several new levels that were previously unobserved or unresolved. In addition, SEP spectra were obtained for six $ãA3″$ levels in $CH35Cl$ and three levels in $CD35Cl$⁠. The derived term energies and rovibrational parameters of the $X̃A1′$ and $ãA3″$ states are in good agreement with theory. The $ãA3″$ triplet spin-spin parameter is vibrational state dependent, and dominated by a second-order contribution from spin-orbit coupling with nearby $X̃A1′$ levels; it therefore provides a sensitive probe of spin-orbit mixing in this system. An analysis of three pairs of interactions between specific $ãA3″$ and $X̃A1′$ levels in $CH35Cl$ affords a pure electronic spin-orbit coupling element of $150cm−1$⁠, in good agreement with theoretical expectations. The derived singlet-triplet gaps, which are the most precise determined to date for any carbene, are compared with the predictions of high level ab initio theory.