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UBC Theses and Dissertations

Hyperfine structure and predissociation of the B ³[pi]₀ + state of bromine Booth, James L.


Investigations have been carried out in bromine of the hyperfine structure of the B ³II₀u+ and X ¹Σg⁺ electronic states and of the predissociation of the B ³ll₀u+ state by the ¹ll₁u dissociative level. The technique of laser induced fluorescence of a molecular beam was used. ⁷⁹Br⁸¹Br hyperfine spectra were recorded for various B - X vibrational bands (v’ ←v”) with v’ = 11 through 17 and v” = 0, 1, and 2, and for various rotational transitions (J’ ← J”) with J’ from 0 to 11 and J” from 0 to 10. As well, the ⁷⁹Br₂ and ⁸¹Br₂ hyperfine spectra of the (13’ — 0”) and (17’ — 2”) bands over the same range of rotational states were measured. The spectra are well described using one X state parameter: the electric quadrupole coupling constant eqQx; and two B state parameters: the electric quadrupole coupling constant eqQB, and the nuclear spin-rotation constant Csr. The results show that eqQB(⁷⁹Br) = (177.0 ± 0.6) MHz for v’ = 11 and increases by approximately 0.5 MHz per vibrational quantum up to (180.6 ± 1.4) MHz for v’ 17. Similarly the ground state electric quadrupole coupling constant, eqQx(⁷⁹Br) (808.1 ± 1.4) MHz for v” = 0 and increases by about 1 MHz per vibrational quantum to (811.4 ± 1.4) MHz for v” = 2. The hyperfine data also provided a check on the accuracy of some of the published rovibronic constant¹ for each isotopomer. In order to reproduce the observed relative spacings of the transitions for all three isotopomers, the published term values, T₀₀, have to be modified ; this can be done by decreasing the published values of T₀₀ for ⁸¹Br₂ and ⁷⁹Br⁸¹Br by (177 ± 8) MHz and (326 ± 8) MHz, respectively. The phase shift technique was applied to the study of the predissociation of the v’ = 13 B ³II₀u⁺ electronic state of bromine. The lifetimes of individual hyperfine levels were ¹S. Gerstenkorn and P. Luc, J. Phys. France 50, 1417 (1989). measured for the rotational states J’ = 0 - 7 (except for J’ 2) for each isotopomer of bromine. Revised values are given for the radiative decay rate Γrad, the gyroscopic predissociation parameter Cv, and the magnetic dipole predissociation parameter av. The first observation of electric quadrupole predissociation is reported and is characterized by a new molecular parameter, bv.

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