ИСТИНА

In the Earth’s, Venusian, and Martian atmospheres, carbon dioxide (CO2) is a strong absorber of infrared radiation, trapping the heat and causing a potent greenhouse effect. Because CO2 molecules lack a permanent dipole moment, the absorption spectrum in the millimeter wavelength range does not exhibit resonant absorption lines and is dictated solely by continuum absorption of bimolecular origin. We conducted an in-depth investigation of mm-wave absorption in pure CO2 and its mixture with argon, seeing those systems as prototypes for more intricate scenarios manifesting as continuum-like troughs in between the dipole-permitted rovibrational bands, which is the case, for example, in water vapor. Our desire to develop a well-grounded understanding of the nature of the continuum motivates the joint theoretical and experimental efforts presented here. The experimental data on the CO2 continuum in the mm-wave range are limited and based on single frequency point observations with large uncertainties [1]. We extend our previously reported results [2], obtained at room temperature only, by recording the spectra of pure CO2 and its mixture with Ar using a resonator spectrometer [3] at temperatures between 268 and 317K and varied pressures ranging from 375 to 1490 Torr. To simulate the collision-induced absorption, we used a semiclassical trajectory-based formalism [4], consistently accounting for the true dimer contribution. The excellent agreement between the simulated and measured CO2-Ar continuum supports both theoretical and experimental approaches. The frequency dependence of continuum absorption notably deviates from the generally utilized quadratic behavior, which was found to be greatly influenced by both metastable and true dimers. Theoretical values of the CO2-CO2 continuum regularly underestimate the observed ones by roughly 20%, which can be tentatively attributed to the assumption of the rigidity of CO2 molecules. For atmospheric studies, we propose a parameterized model for the frequency and temperature dependence of the CO2-Ar continuum. The work is supported by the RSF project 22-17-00041. References: [1] A. Bauer, et al. J. Mol. Spectrosc. 176, 45, 1996 [2] T. A. Odintsova, et al. J. Quant. Spectrosc. Rad. Transf. 258, 107400, 2021. [3] M.A. Koshelev et al. IEEE Trans. Terahertz. Sci. Technol. 8 No 6, 773, 2018 [4] D. N. Chistikov et al. J. Chem. Phys. 155, 064301, 2021.