High-Accuracy ${\mathrm{CO}}_2$ Line Intensities Determined from Theory and Experiment

Atmospheric ${\mathrm{CO}}_2$ concentrations are being closely monitored by remote sensing experiments which rely on knowing line intensities with an uncertainty of 0.5% or better. Most available laboratory measurements have uncertainties much larger than this. We report a joint experimental and theoretical study providing rotation-vibration line intensities with the required accuracy. The ab initio calculations are extendible to all atmospherically important bands of ${\mathrm{CO}}_2$ and to its isotologues. As such, they will form the basis for detailed ${\mathrm{CO}}_2$ spectroscopic line lists for future studies.

Figure 1

Ab initio intensities (this work) and literature values relative to the present measurements versus the rotational quantum number $m$. Error bars represent $\pm 1$ standard deviation. The average, weighted (based on the inverse of the ${\mathrm{RSU}}^2$) relative difference between the calculations and the present measured values equals-0.33% (indicated by the horizontal line) and has a standard error of 0.05%. This comparison gives a root-mean-square deviation of 0.23% consistent with the measurement RSU. Data sources are CDSD [44], HITRAN [9], LPPM [18], and GSMA [18].

Figure 2

Ab initio line intensities (this work) for the (20012)–(00001) band of the ${}^{12}\mathrm{C}{{}^{16}\mathrm{O}}_2$ molecule at 296 K compared to the measurements of Casa et al. in 2007 [19] (blue triangles) and 2009 [20] (orange diamonds), and the single 2011 measurement of Wuebbeler et al. [12] (red circle).