Accurate rovibrational spectroscopy of relevant astrochemical complexes: CH₄⋯CH₄, CH₄⋯N₂ and CH₄⋯Ar

Rovibrational spectroscopic properties of CH₄⋯CH₄, CH₄⋯N₂, and CH₄⋯Ar weakly bound complexes are relevant to astrophysics and astrochemistry, with particular interest to research on Titan's atmosphere. Different methodologies were applied to achieve the high accuracy required to fill the data gap in the literature of these complexes, particularly regarding their most stable configuration. The strategy is based on the generation of potential energy curves (PECs) using the all-electron CCSD(T) method with Dunning basis sets (aug-cc-pVXZ, where X  = D, T, Q, and 5), applying counterpoise correction (CP) for basis set superposition error (BSSE) and performing extrapolation to the complete basis set (CBS) limit, evaluating five extrapolation schemes. These curves were fitted with three functions, and the spectroscopic properties were obtained. Additionally, the decomposition lifetimes of the complexes as a function of temperature were determined. Therefore, the results overcame many published theoretical results and agreed with the experimental data available in the literature. Furthermore, it is worth emphasizing that the decomposition lifetime results correspond closely to the information on the Titan atmosphere, thereby indicating the reliability of the theoretical model in accurately describing this particular property. Moreover, most of these results, generated with the described methodology, were not found in the literature for the three systems to the best of our knowledge.