Experimental and theoretical studies of the near-infrared spectrum of bromomethylene

Abstract

New measurements in the à 1A″–X̃ 1A′ band system of monobromomethylene (HCBr) at near-infrared wavelengths are reported. Rotationally resolved spectra of HCBr and DCBr for both naturally occurring Br isotopes are analyzed and provide accurate energies for the low-lying bending vibrational levels in both the à and X̃ states. The experimental results are compared to extensive ab initio calculations of these two states and the low-lying ã 3A″ state. The ab initio T00 value for the ÖX̃ system is calculated within 500 cm−1 of the experimental results. For the triplet state, T00 (α̃–X̃) was calculated to be 1833 cm−1. The measurements of the bending intervals in the X̃ 1A′ state suggest that this is about 250 cm−1 too low. With this shift and inclusion of spin–orbit coupling between the ã and X̃ states, the calculated bending vibrational levels in the X̃ state reproduce the observations, and the calculations make testable predictions of the position of the triplet and other singlet state vibronic levels. Combining the experimental and computational results, we estimate the triplet, T00(ã–X̃), excitation energy to be 2028 cm−1.