Frequency comb referenced spectroscopy of <i>A</i>–<i>X</i> 0–0 transitions in SH

We report absolute transition frequencies for the allowed transitions from X2?3/2, v? = 0, J? 3/2 rovibronic ground state of 32S1H to A2?+, v? 0 vibronic state. The have been determined with an uncertainty less than 1 MHz, representing a more 1000-fold improvement over previous measurements. Spectral traces are measured by scanning frequency comb stabilized continuous-wave spectroscopy laser molecular and detecting laser-induced fluorescence SH molecules in highly collimated beam. To determine frequencies, fit quantum-mechanical model that accounts saturation effects shifts due quantum interference. also provides estimates predissociation rate excited-state levels. Weighted averages hyperfine-resolved computed order enable comparisons measurements where hyperfine structure is not resolved. These hyperfine-averaged indicate were about ?2.1 GHz (0.07 cm?1) too high. Finally, using effective Hamiltonian model, resulting precise spectroscopic constants.