Near-infrared spectroscopy of bromomethylene in a slit-jet expansion

Several rotational subbands of the bromomethylene (HCBr) and deuterated bromomethylene (DCBr) origin band in the region of 830-840 nm have been recorded under slit-jet cooled conditions that result in rotational and translational temperatures of approximately 20 K. The radical was formed by 193-nm laser photolysis of bromoform in the early stages of the expansion and detected by absorption of a single-frequency Ti:sapphire ring laser. The spectral simplification achieved compared to earlier measurements at ambient temperature allowed a nearly complete rotational analysis. The data were combined with additional measurements at room temperature in order to determine rotational constants and estimate a structure for the radical in its ground state. With the exception of K′ = 0, the excited state levels were found to suffer multiple perturbations due to interactions with the manifold of excited X state levels caused by Renner-Teller and anharmonic coupling. Atomic bromine transitions from the ⁴P_5/2 level at 63 400 cm^-1 were also observed in the source following absorption of at least two 193-nm photons by the precursor.