High-precision spectroscopy of molecular iodine: From optical frequency standards to global descriptions of hyperfine interactions and associated electronic structure.

摘要

A widely tunable and high-resolution spectrometer based on a frequency-doubled Ti:sapphire laser is used to explore sub-Doppler transitions of molecular iodine in the wavelength range 523--498 nm. We investigate the natural width of the hyperfine components at various transitions and its wavelength dependence is mapped out in this region. The narrowest natural width observed is ∼52 kHz near 508 nm. The observed excellent signal-to-noise ratio should lead to high-quality optical frequency standards that are better than those of the popular 532-nm system. In addition, we employ a self-referenced femtosecond optical comb to measure the absolute frequency of the length standard at 514.67 nm, which is based on the a3 hyperfine component of transition P(13) 43-0. This technique improves the precision of the frequency measurement by two orders of magnitude as compared with previous wavelength-based results.; The hyperfine spectra of B ← X transitions in the wavelength range 500--517 nm are investigated systematically. Four effective hyperfine parameters, eqQB, CB, dB, and delta B, are determined for an extensive number of rovibrational levels spanning the intermediate region 42 upsilon' 70 in the B0+u (3piu) state. Near vibrational levels upsilon ' = 57--60, the 1g( 1pig) electronic state strongly perturbs the B0+u (3piu) state through rotational coincidence, leading to effects such as abnormal variations in the hyperfine parameters and strong u-g mixing recorded at the transition P(84) 60-0. Various perturbation effects in the B0+u (3piu) state identified so far are summarized.; We have also performed a high-resolution analysis of the six electronic states that share the same dissociation limit with the excited electronic state B0+u (3piu) in molecular iodine. These six states are coupled to the B0+u (3piu) state via hyperfine interactions. The four hyperfine parameters are calculated using available potential energy curves and wave functions constructed from the separated-atom basis set. We obtain a maximum separation of the respective contributions from all six electronic states and compare each individual contribution with high-precision spectroscopic data, allowing an independent verification of the relevant electronic structure.