We report new measurements of the hyperfine spectra of B←X transitions in the wavelength range 500–517 nm. Four effective hyperfine parameters, eqQ<sub>B</sub>, C<sub>B</sub>, d<sub>B</sub>, and δ<sub>B</sub>, are determined for an extensive number of rovibrational levels spanning the intermediate region 42≤v<sup>′</sup>≤70 in the electronically excited B0<sub>u</sub><sup>+</sup>(<sup>3</sup>Π<sub>u</sub>) state. Second-order perturbation accounts for most of the observed rovibrational dependence of the hyperfine interactions. In addition, it was found that, near vibrational levels v<sup>′</sup>=57–60, the 1<sub>g</sub>(<sup>1</sup>Π<sub>g</sub>) electronic state strongly perturbs the <i>B</i> state through rotational coincidence, leading to effects such as abnormal variations in the hyperfine parameters and strong u–g mixing recorded for the transition P(84)60–0. Various perturbation effects in the <i>B</i> state identified so far are summarized. Also, the radial dependence of the hyperfine interactions was examined by removal of the vibrational average in the hyperfine parameters.
© 2004 Optical Society of America
(020.2930) Atomic and molecular physics : Hyperfine structure
(300.6190) Spectroscopy : Spectrometers
(300.6390) Spectroscopy : Spectroscopy, molecular
(300.6460) Spectroscopy : Spectroscopy, saturation
Lisheng Chen, Wang-Yau Cheng, and Jun Ye, "Hyperfine interactions and perturbation effects in the B0u+(3Πu) state of 127I2," J. Opt. Soc. Am. B 21, 820-832 (2004)