Laser Transient Absorption Spectroscopy of Bromomethylene

Area of Science:

• Molecular Spectroscopy
• Quantum Chemistry
• Chemical Physics

Background:

• Bromomethylene (HCBr) is a small molecule with interesting electronic and rotational properties.
• Previous studies have investigated its A1A" state, but some assignments required reassessment.

Purpose of the Study:

• To obtain and assign new high-resolution spectra of the A1A" <-- X1A' transition of HCBr.
• To analyze the rotational structure of specific vibrational bands (2(1)0 and 2(2)0) for HCBr and DCBr isotopomers.
• To reassess previous assignments and investigate potential perturbations in the A1A" state.

Main Methods:

• Transient laser absorption spectroscopy at near-infrared wavelengths.
• Observation and detailed assignment of c-type rotational branches.
• Analysis of spectral data for naturally occurring bromine isotopes.

Main Results:

• New high-resolution spectra of the 2(1)0 band of HCBr and the 2(2)0 band of DCBr were obtained and assigned.
• The lower singlet state was found to be isolated, with no evidence of triplet state perturbations.
• Rotational constants were derived for ground-state isotopomers, enabling estimation of structural parameters.
• A barrier to linearity for the A1A" state was estimated at 13,590 cm-1 above the ground state zero-point level.

Conclusions:

• The study provides a reassessment of previous assignments for the A1A" state of HCBr.
• The vibrational levels studied exhibit nonlinear rotational structure, contrasting with prior observations.
• The findings contribute to a better understanding of the electronic structure and molecular geometry of bromomethylene.