Knowledge Bank

Bromine dimer has been studied by many researchers in various wavelength regions. The $A3\Pi 1u$ and $X1\Sigma g+$ states have been well observed using magnetic rotation spectroscopy, by laser-induced fluorescence,, J.~Mol.~Spectrosc.\ 200, 104 (2000).}$,$, to be published.} by laser absorption,, Columbus Meeting, paper WH02 (2005).} by Fourier transform absorption,, J.\ Physique, 48, 1685 (1987).} and by UV emission., J.~Mol.~Spectrosc.\ 96, 247 (1982).}~ This yields a data set consisting of 16916 transitions in which the observed vibrational levels for the $X1\Sigma g+$ and $A3\Pi 1u$ states span 83% and 99% of the potential well depths, respectively, with the highest observed vibrational level of the $A3\Pi 1u$ state lying only 2 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ below the dissociation limit. In order to provide the most compact and comprehensive description of these data, and the ability to make reliable predictions outside their range, we have chosen to perform a "direct potential fit'' (DPF), rather than a conventional Dunham-expansion analysis. In particular, accurate analytic potential energy functions for the $A3\Pi 1u$ and $X1\Sigma g+$ states are determined from a combined-isotopologue DPF analysis that also yields the electronic isotope shift, the $\Omega$-doubling radial strength function, and an experimental value for the long-range inverse-power $C5$ constant of the $A3\Pi 1u$ state, as well as centrifugal Born-Oppenheimer Breakdown (BOB) functions for both states. To reveal characteristics of the $A3\Pi 1u$ state, band constants calculated from these potentials are compared with those determined from a conventional parameter-fitting analysis reported by Coxon.