The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr3 vapor and H2 or D2 in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra. HBBr has an extensive band system in the red which involves a linear-bent transition between the two Renner-Teller components of what would be a 2Π state at linearity. We have used high level ab initio theory to calculate potential energy surfaces for the bent 2A′ ground state and the linear 2A″Π excited state and we have determined the ro-vibronic energy levels variationally, including spin orbit effects. The correspondence between the computed and experimentally observed transition frequencies, upper state level symmetries, and H and B isotope shifts was used to make reliable assignments. We have shown that the ground state barriers to linearity, which range from 10 000 cm−1 in HBF to 2700 cm−1 in BH2, are inversely related to the energy of the first excited 2Σ (2A′) electronic state. This suggests that a vibronic coupling mechanism is responsible for the nonlinear equilibrium geometries of the ground states of the HBX free radicals.

Document Type


Publication Date


Notes/Citation Information

Published in The Journal of Chemical Physics, v. 144, issue 23, 234309, p. 1-11.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.

The following article appeared in The Journal of Chemical Physics 144, 234309 (2016) and may be found at https://doi.org/10.1063/1.4953771.

Digital Object Identifier (DOI)


Funding Information

This material is based upon work supported by the National Science Foundation under Grant No. CHE-1106338. R.T. acknowledges financial support from the University of Bologna.

Related Content

See supplementary material at https://doi.org/10.1063/1.4953771 E-JCPSA6-144-038623 for a table of the expansion coefficients of the HBBr potential energy surfaces.

epaps_hbbr.doc (84 kB)
EPAPS Supplementary Material