The absorption spectrum of H2S between 9540 and by intracavity laser absorption spectroscopy with a vertical external cavity surface emitting laser

An Intracavity Laser Absorption Spectrometer (ICLAS) based on a Vertical External Cavity Surface Emitting Laser (VECSEL) has been used to record the absorption spectrum of H2S between 9540 and 10 000 cm −1 with pressures up to 122 Torr (160.5 hPa) and equivalent absorption path lengths up to 45 km. More than 1600 absorption lines were attributed to the transitions reaching the highly excited (40±,0), (30±,2), and (11+,4) states (local mode notation). The existing information relative to the (40±,0) local mode bright pair at 9911.02 cm −1 was considerably enlarged, while the other states are reported for the first time. Eight hundred and ninety two precise energy levels were derived, including 181 and 28 levels for the H 2 34 S and H 2 33 S minor isotopomers, respectively. These energy levels were fitted using a Watson-type rotational Hamiltonian and the spectroscopic parameters were obtained, yielding an rms deviation of 0.006 cm −1 for the H 2 32 S species—close to the experimental accuracy. The dark states—(20+,4) and (11+,4)—at 9647.77 and 9744.88 cm −1 , respectively, were found to perturb the observed energy levels and were then included into the final energy levels modeling. The (40±,0) states are very close to the local mode limit, i.e., with a mostly identical rotational structure. The (30±,2) states are separated by 0.077 cm −1 and this separation holds for most of the rotational sublevels. The resonance interactions between the three local mode pairs—(40±,0), (30±,2), and (20±,4)—and the (11+,4) state affect in some cases specifically one of the component of the pair and then the energy separation of the corresponding near degenerate rotational levels. Line intensities were obtained on the basis of the relative intensities measured by ICLAS and from absolute values of the stronger lines measured separately by Fourier Transform Spectroscopy associated with a multipass cell. The transition intensities could be successfully modeled and the integrated band intensities are given and discussed.