Discovery of multiple bands of isotopic CO2 in the prime spectral regions used when searching for CH4 and HDO on Mars

We present new measurements of vibrational band systems of isotopic carbon dioxide (CO2) with multiple strong lines in the wavelength region 3.3-3.7 μm. In our ground-based searches for methane (CH4) and other biomarker gases on Mars, we discovered two new vibrational band systems that we identify as the previously unknown ν2+ν3 band of 16O12C18O and the 2ν1 band of the rare isotope 16O13C18O. We also extended and provide refined spectroscopic constants for the 2ν1 band of 16O12C17O, detecting 38 new lines. The newly discovered 2ν1 band of 16O13C18O at 3.7 μm and the 2ν1 band of 16O12C17O at 3.6 μm extend over the prime spectral region used when searching for deuterated water (HDO) and formaldehyde (H2CO) on Mars. The ν2+ν3 band of 16O12C18O at 3.3 μm interferes with the ν3 band of CH4 at 3.3 μm. If unrecognized, even weak bands of CO2 can obscure searches for trace gases on Mars, so it is important to quantify them. Here, we report molecular parameters from the measured line positions that agree well with values calculated from the known energy levels of these isotopologues, and we provide absolute band strengths for each system.