Line parameters for the 01111–00001 band of 12C 16O 18O from SOIR measurements of the Venus atmosphere

Abstract

CO 2 is the major constituent of the atmosphere of Venus. Absorption lines due to its 12C 16O 18O isotopologue have been observed for the first time in Venus spectra in the 2930–3015 cm −1 spectral region, where the HITRAN database does not contain any line from this isotopologue. The measurements were performed by the SOIR instrument, which is part of the SPICAV/SOIR instrument on board the Venus Express mission of ESA. SOIR measured the atmospheric transmission of the upper atmosphere of Venus ( z>70 km) by performing a solar occultation experiment using the atmosphere as a gigantic absorption cell. The identification of this newly observed band was first made recently from Mars atmosphere observations by US colleagues. We have made independent theoretical calculations of the positions of the lines of this new 01111–00001 absorption band, which coincide perfectly with the positions of the observed lines. Assuming an oxygen isotopic ratio similar to the one measured previously in the lower atmosphere of Venus, the line strengths of each observed line are deduced and listed.