1,4,5Įxtracting information about the physical conditions and chemical composition of comets, and estimating the abundance of molecules, relies on modeling the observational spectra. 3 These observations led to new insights about the composition of cometary ices and atmospheres, which present a huge diversity of molecules including H 2O, CO and CO 2, CH 3OH and CH 4. 1 One of the most significant studies was carried out by the ROSETTA spacecraft, which performed in situ observations of comet 67P/Churyumov–Gerasimenko. 2 Numerous observations of comets have been performed, covering a wide range of wavelengths from ultraviolet, optical, infrared, to radio. 1 In addition, astronomical models show that various volatile species in Earth's atmosphere, especially noble gases, might have originated from comets. This leads to valuable information about the physical conditions prevailing during planets formation. Their ice nuclei contain molecules formed at the early stages of planetary formation, and performing spectroscopic observations of the coma, the temporary gaseous atmosphere of a comet, gives insights into the composition of the nucleus. The use of these new collisional data should help in accurately deriving the physical conditions in CO-dominated comets.Ĭomets are valuable sources of information about the evolution of the solar system. Due to the high cost of the calculations, we also investigated the possibility of using an alternative statistical approach to extend our calculations both in terms of rotational states and temperatures considered. In comparison with data available in the literature, significant differences were found, especially for the dominant transitions. Cross sections were calculated for energies up to 800 cm −1, and excitation rate coefficients were derived for temperatures up to 100 K. Using the quantum coupled states approach, cross sections and rate coefficients are provided between the first 37 rotational states of the CO–CO system. This paper presents new scattering calculations for the collisional energy transfer in CO–CO collisions. For comets at large heliocentric distances, the production of carbon monoxide (CO) gas is found to be larger than the production of water, so that molecular excitation will be induced by collisions with CO molecules.
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Hence, radiative and collisional properties of molecules are needed to correctly model molecular spectra. In such environments, densities can be so low ( n ≪ 10 10 cm −3) that local thermodynamical equilibrium conditions cannot be maintained. An accurate determination of the physical conditions in astrophysical environments relies on the modeling of molecular spectra.