The chemistry of carbenes is fascinating, as the divalent carbon gives rise to singlet and triplet states with similar energy but very different chemical reactivity. A central issue in carbene chemistry has been determining the singlet-triplet energy gap. Our group has approached this using laser based techniques, where an excited singlet state is pumped and transitions to thelow-lying triplet state detected by spontaneous or stimulated emission.
Displayed below are single vibronic level emission spectra of CHCl and CDBr, which show transitions to vibrational levels of the low-lying triplet state. The value for ΔEST derived from these spectra are in nearly quantitative agreement with high level ab initio predictions.
We are also presently pursuing high resolution studies of spin-orbit mixing in the halocarbenes using Stimulated Emission Pumping (SEP) spectroscopy. Other recent carbene studies include fluorescence excitation and emisson spectra of CBr2 which have led to a reassignment of the position of the electronic origin.