Analysis and modeling of combination bands of sulfur hexafluoride 32SF6 based on global fits. Update of the SHeCaSDa database

Abstract

Sulfur hexafluoride is a powerful greenhouse gas of industrial origin. Remotesensing detection of this heavy species requires a detailed knowledge of its infrared absorption spectra that features many hot bands at room temperature. It is thus necessary to study many of its rovibrational levels which are implied in such hot band transitions. Based on our previous results reporting global fits of many rovibrational bands [M. Faye at al., J. Quant. Spectrosc. Radiat. Transfer 190, 38-47 (2017)], we present here detailed analyses of three combination bands, namely ν 1 + ν 4 , ν 2 + ν 6 and ν 5 + ν 6. The ν 2 + ν 6 combination band has been already investigated some years ago, but the present analysis represents a strong improvement; the two other bands are analyzed in detail for the first time. The results contribute to improve the simulation of hot bands in the strongly absorbing ν 3 and ν 4 regions and they have been used to update the SHeCaSDa database (http://vamdc.icb.cnrs.fr/PHP/shecasda.php).

The 2020 edition of the GEISA spectroscopic database

“….Contrary to the species describe in the section 2, SF6 has not been updated in the current version of GEISA, although new data were provided by Ke et al from the Dijon's database SheCaSDa [168]. Indeed, recent data from Nikitin et al [169] consisting of a complete line list based of extensive ab initio calculations (from TheoReTS database [170]) leads to significantly different results.…”

Towards a complete elucidation of the ro-vibrational band structure in the SF6 infrared spectrum from full quantum-mechanical calculations

“…, recently updated with the set 32 (ν 1 + ν 4 , ν 2 + ν 6 , ν 5 + ν 6 ). All these combination bands and overtones are of key importance for computing a part of HBs falling in the strongly absorbing ν 3 and ν 4 regions.…”

“…This permitted diminishing the density of line by removing high-J transitions as well as many HBs. In turn, a large amount of information concerning HBs is clearly missing at 296 K. For this reason, the recent line list in SHeCaSDa SF 6 database 32 as well as the closely related HITRAN 30 and GEISA 31 compilations do not contain enough line parameters to reproduce and explain the vibrational band structure at 296 K, in particular around ν 3 . Completeness of rovibrational bands will be thus the key requirement for a successful modelling of the radiative transfer.…”

“…Contribution of the cold (CB) and hot (HB) bands are plotted and the strongest bands are indicated (the complete list can be found in Supplementary Material S 2 ). A comparison with the SHeCaSDa database32 is also given in the range 590−640 cm −1 . Comparison of theoretical absorption spectra of 32 SF 6 + 33 SF 6 + 34 SF 6 with experimental medium resolution PNNL records62 at room temperature the range 925−1005 cm −1 .…”

“…Summary of the final line lists for 32 SF 6 and comparison with the SHeCaSDa database32 . The number of strong and quasi-continuum (QC) lines (#lines) as well as the integrated intensities (∑lines) are indicated.…”