Single vibronic level emission spectroscopy of the [formula omitted] system of dibromocarbene

Abstract

Following the development of an improved discharge recipe for production of dibromocarbene (CBr 2), and an extensive spectroscopic survey of the A ˜ 1 B 1 ← X ˜ 1 A 1 system that has led to a revision in the position of the origin, we have recorded single vibronic level (SVL) emission spectra of C 79Br 81Br and C 81Br 2 which probe the vibrational structure of the X ˜ 1 A 1 state up to ∼7000 cm −1 above the vibrationless level. These spectra reveal many previously unassigned levels. In the region between ∼3600 and 5900 cm −1, or between the singlet-triplet gap proposed by Hsu et al. [H.-J. Hsu, W.-Z. Chang, B.-C. Chang, Phys. Chem. Chem. Phys. 2005, 7, 2468–2473] to that predicted by theory, we find that ∼90% of the lines can be assigned to X ˜ 1 A 1 levels within three standard deviations of our Dunham expansion fit, suggesting that the vast majority of emission lines terminate on levels of the singlet state. A nearly complete set of vibrational parameters was determined for the X ˜ 1 A 1 state; the derived parameters are in good agreement with recent ab initio predictions.