High-resolution Infrared Spectroscopy Of Jet Cooled Hcbr Singlet Bromocarbene Diradical

First high-resolution mid infrared rovibrational spectral data on jet cooled bromocarbene (HCBr) diradical are obtained using quantum shot noise limited laser absorption methods. The HCBr diradical is generated by coflowing bromoform (HCBr$_{3}$) in a mixture of Ne, He, and H$_{2}$ through a pulsed slit discharge beam source and is subsequently cooled down to approximately 40 K in a slit-jet supersonic expansion. Interestingly, optimization of the HCBr radical requires the presence of H$_{2}$, presumably due to decomposition of HCBr$_{3}$ by H atom chemistry in the discharge. Rotationally resolved absorption spectra of the CH stretch \nub{1} = 1 $\leftarrow$ 0 fundamental are analyzed, resulting in precise determination of ground and excited state rovibrational constants for both $^{79}$Br and $^{81}$Br isotopologues. The results for the ground state are in good agreement with previous high resolution near IR electronic studies in the Sears group\footnote{Journal of Molecular Spectroscopy 202, 131–143 (2000)}. The \nub{1} band origin is now unambiguously assigned at 2799 cm$^{-1}$, which agrees well with previous LIF/dispersed fluorescence studies of Reid and coworker\footnote{J. Chem. Phys. 124, 134302 (2006)}