Abstract
We report absolute transition frequencies for the allowed transitions from the X2Π3/2, v″ = 0, J″ = 3/2 rovibronic ground state of 32S1H to the A2Σ+, v' = 0 vibronic state. The frequencies have been determined with an uncertainty of less than 1 MHz, representing a more than 1000-fold improvement over previous measurements. Spectral traces are measured by scanning a frequency comb stabilized continuous-wave spectroscopy laser over the molecular transitions and detecting laser-induced fluorescence from SH molecules in a highly collimated molecular beam. To determine the absolute transition frequencies, the traces are fit with a quantum-mechanical model that accounts for saturation effects and shifts due to quantum interference. The model also provides estimates of the predissociation rate of the excited-state levels. Weighted averages of the hyperfine-resolved transition frequencies are computed in order to enable comparisons to measurements where the hyperfine structure is not resolved. These hyperfine-averaged frequencies indicate that the absolute transition frequencies determined in previous measurements were about ∼2.1 GHz (0.07 cm-1) too high. Finally, the measured transition frequencies are fit using an effective Hamiltonian model, resulting in more precise estimates of the spectroscopic constants.
Highlights
Ultraviolet absorption features of the mercapto radical, SH, have recently been observed in several extraterrestrial systems, most distinctly in interstellar gas clouds1 and tentatively in the solar atmosphere2 and in the atmosphere of a hot Jupiter exoplanet.3 These observations have helped motivate the creation of an improved line list that covers the A2Σ ← X2Π electronic transitions responsible for these features.4 The absolute accuracy of the transition frequencies in this new list depends almost entirely on the accuracy of the transition frequencies determined nearly seven decades ago by Ramsay5 using a grating spectrometer
While the 0.03-cm−1 absolute uncertainty reported in this earlier work was state-of-theart for the time, modern laser spectroscopy techniques can provide much more precise values for these transition frequencies, when combined with an optical frequency comb for absolute frequency calibration
We report the absolute transition frequencies for all allowed transitions from the X2Π3/2, v′′ = 0, J′′ = 3/2 rovibronic ground state levels of 32S1H to the A2Σ+, v′ = 0 vibronic state
Summary
Ultraviolet absorption features of the mercapto radical, SH, have recently been observed in several extraterrestrial systems, most distinctly in interstellar gas clouds and tentatively in the solar atmosphere and in the atmosphere of a hot Jupiter exoplanet. These observations have helped motivate the creation of an improved line list that covers the A2Σ ← X2Π electronic transitions responsible for these features. The absolute accuracy of the transition frequencies in this new list depends almost entirely on the accuracy of the transition frequencies determined nearly seven decades ago by Ramsay using a grating spectrometer. Ultraviolet absorption features of the mercapto radical, SH, have recently been observed in several extraterrestrial systems, most distinctly in interstellar gas clouds and tentatively in the solar atmosphere and in the atmosphere of a hot Jupiter exoplanet.. Ultraviolet absorption features of the mercapto radical, SH, have recently been observed in several extraterrestrial systems, most distinctly in interstellar gas clouds and tentatively in the solar atmosphere and in the atmosphere of a hot Jupiter exoplanet.3 These observations have helped motivate the creation of an improved line list that covers the A2Σ ← X2Π electronic transitions responsible for these features.. Using a narrow-linewidth continuous-wave spectroscopy laser referenced to an optical frequency comb, the transition frequencies have been determined with an uncertainty of less than 1 MHz, corresponding to a more than 1000-fold reduction of the overall uncertainty. In addition to the absolute transition frequencies, we use the observed linewidths to estimate the decay rates due to predissociation in the excited state levels; the resulting rates agree with the A state lifetime previously reported by Ubachs et al.
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