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The linear Stark effect measured in the ν2/ν4 dyad of SnH4 by Doppler-free infrared–infrared double resonance spectroscopy has been analyzed. Fifteen double resonance signals in the vibrationally excited state and 12 previously reported signals in the ground state have been fitted simultaneously to an effective Stark Hamiltonian. The centrifugal distortion moment μ0 and the two vibration-induced moments μ44 and μ24 are determined to be μ0=1.499(11)×10-5 D, μ44=-1.317(42)×10-2 D, and μ24=3.94(23)×10-2 D. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Sulfur hexafluoride is an important molecule for modeling thermophysical and polarizability properties. It is also a potent greenhouse gas of anthropogenic origin, whose concentration in the atmosphere, although very low is increasing rapidly; its global warming power is mostly conferred by its strong infrared absorption in the ν3 S–F stretching region near 948 cm−1. This heavy species, however, features many hot bands at room temperature (at which only 31% of the molecules lie in the ground vibrational state), especially those originating from the lowest, v6 = 1 vibrational state. Unfortunately, the ν6 band itself (near 347 cm−1), in the first approximation, is both infrared- and Raman-inactive, and no reliable spectroscopic information could be obtained up to now and this has precluded a correct modeling of the hot bands. It has been suggested theoretically and experimentally that this band might be slightly activated through Coriolis interaction with infrared-active fundamentals and appears in high pressure measurements as a very faint, unresolved band. Using a new cryogenic multipass cell with 93 m optical path length and regulated at 163 ± 2 K temperature, coupled to synchrotron radiation and a high resolution interferometer, the spectrum of the ν6 far-infrared region has been recorded. Low temperature was used to avoid the presence of hot bands. We are thus able to confirm that the small feature in this region, previously viewed at low-resolution, is indeed ν6. The fully resolved spectrum has been analyzed, thanks to the XTDS software package. The band appears to be activated by faint Coriolis interactions with the strong ν3 and ν4 fundamental bands, resulting in the appearance of a small first-order dipole moment term, inducing unusual selection rules. The band center (ν6 = 347.736707(35) cm−1) and rovibrational parameters are now accurately determined for the v6 = 1 level. The ν6 perturbation-induced dipole moment is estimated to be 33 ± 3 μD and the ν6 integrated intensity to be 0.0035 km mol−1. [ABSTRACT FROM AUTHOR]

Highly symmetrical molecules such as CH4, CF4 or SF6 are known to be atmospheric pollutants and greenhouse gases. High-resolution spectroscopy in the infrared is particularly suitable for the monitoring of gas concentration and radiative transfers in the earth's atmosphere. This technique requires extensive theoretical studies for the modeling of the spectra of such molecules (positions, intensities and shapes of absorption lines). Here, we have developed powerful tools for the analysis and the simulation of absorption spectra of highly symmetrical molecules. These tools have been implemented in the spherical top data system (STDS) and highly-spherical top data system (HTDS) software available at http://www.u-bourgogne.fr/LPUB/shTDS.html. They include a compilation of modeled data obtained during the last 20 years. An overview of our latest results in this domain will be presented. [ABSTRACT FROM AUTHOR]