High sensitivity CRDS of CO2 in the 1.18 µm transparency window. Validation tests of current spectroscopic databases. (May 2020)

• Record Type: Journal Article
• Authors: Karlovets, E.V.; Kassi, S.; Campargue, A.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 247(2020)
• Publication Date: 2020-05
• Subjects: Carbon dioxide -- CO2 -- Transparency windows -- Venus, HITRAN, CDSD; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2020.106942
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: High sensitivity CRDS of CO2 in the 1.18 µm transparency window of interest for Venus. 669 transitions assigned to 18 bands of three CO2 isotopologues. Very weak lines with intensity value smaller than 10 −30 cm/molecule are detected. Practically no previous observations were available in the region. Some deficiencies are evidenced in the HITRAN2016 and CDSD2019 lists. Abstract: The very weak absorption spectrum of natural CO2 is studied at high sensitivity near 1.18 µm. The investigated region corresponds to a transparency window of particular interest for Venus. Low pressure (10 Torr) spectra are recorded with unprecedented sensitivity in the 8311–8679 cm −1 interval. A noise equivalent absorption, α min, on the order of 5 × 10 −12 cm −1 is achieved using a cavity ring down spectrometer (CRDS) coupled with a self-referenced frequency comb. 669 lines are accurately measured and rovibrationnally assigned to 15 bands of the three first carbon dioxide isotopologues, 12 C 16 O2, 13 C 16 O2 and 16 O 12 C 18 O. For all but one band, line intensities are smaller than 10 −28 cm/molecule at 296 K and the weakest lines have intensity as low as 5 × 10 −31 cm/molecule. In the large 8310–8645 cm −1 interval where no CO2 absorption lines were previously detected, about 500 lines are measured. In spite of the weakness of the considered transitions, line centers could be accurately determined and spectroscopic parameters are determined from standard band-by-band fit of the line positions (typical rms deviations are 5 × 10 −4 cm −1 ). These newly observed bands provide critical validation tests for the most recent spectroscopic databases of carbon dioxide. The comparison to the recent updated version of the Carbon Dioxide Spectroscopic Databank (CDSD2019), to the current HITRAN2016 database and ab initio line lists is presented. The CDSD and HITRAN positions deviate from the measurements by less than 0.01 cm −1 . Measured line intensities show an overall good agreement in particular with ab initio values but reveal that a few bands have inaccurate intensities in HITRAN2016 and CDSD2019. Three very weak bands are missing in CDSD2019. The reported experimental information will help to improve the quality of the CO2 spectroscopic databases in the region. Graphical abstract: Image, graphical abstract