Resolving the forbidden band of SF6

Area of Science:

• Molecular spectroscopy
• Atmospheric chemistry
• Quantum mechanics

Background:

• Sulfur hexafluoride (SF6) is a potent greenhouse gas with significant infrared absorption.
• Hot bands in SF6 spectra complicate accurate thermophysical and polarizability modeling.
• The ν6 band of SF6 is infrared and Raman inactive, hindering spectroscopic analysis.

Purpose of the Study:

• To obtain reliable spectroscopic information for the ν6 band of sulfur hexafluoride.
• To accurately determine the band center and rovibrational parameters for the v6 = 1 level.
• To understand the activation mechanism and intensity of the ν6 band for improved atmospheric modeling.

Main Methods:

• Utilized a cryogenic multipass cell (93 m path length) at 163 K.
• Employed synchrotron radiation and a high-resolution interferometer for spectral recording.
• Analyzed the far-infrared spectrum using the XTDS software package.

Main Results:

• Confirmed the ν6 band of SF6 at approximately 347 cm⁻¹.
• Determined the band center to be 347.736707(35) cm⁻¹ and rovibrational parameters for the v6 = 1 level.
• Estimated the perturbation-induced dipole moment to be 33 ± 3 μD and integrated intensity to be 0.0035 km mol⁻¹.

Conclusions:

• The ν6 band is activated by Coriolis interactions with ν3 and ν4 fundamental bands.
• Accurate spectroscopic data for the ν6 band enable better modeling of SF6's atmospheric properties.
• This study provides critical data for understanding SF6 as a greenhouse gas.