New ab initio calculations and collisional properties of closed shell NCCP (1Σ+) by collisions with He (1S) Ritika and T.J. Dhilip Kumar Department of Chemistry, Indian Institute of Technology, Ropar, India In the last century, the knowledge of the interstellar medium (ISM) has changed significantly. From the concept of vacuum between stars, modern astrochemistry has helped us gain a thorough knowledge of the main physical and chemical processes in various interstellar environments. By the 1960s, it had become clear that the ISM is host to a rich chemistry. In a typical interstellar cloud, the two processes that are more important for transitions between internal levels of molecules are radiative and collisional in nature with the most widespread neutral species (H, He and H 2 ) [1]. The analysis of the collisional processes requires information of the rate coefficients of the discovered interstellar molecules with the most abundant colliders in the ISM, which are usually unknown. Information of the collisional rate between the fixed quantum levels is necessary for the analysis of observed spectra. This makes the study of molecular collision dynamics of the utmost significance using quantum chemistry methods. The present work deals with the quantum dynamics of collisions of interstellar molecule, NCCP [2] with Helium (He). To begin with the construction of potential energy surface (PES), dynamical studies are carried out for collisions occurring at low temperatures. An ab initio PES of NCCP-Hecomplex has a well-depth of -46.40 cm 1 at the CCSD(T)-F12a/aug-cc-pVTZ level of theory. Utilizing the multipole expansions, collisional cross-sections have been determined for total energies up to 550 cm -1 by close-coupling method that depicts high resonances below 80 cm -1 . Rotational deexcitation rates are further worked out with averaging the calculated cross-sections at temperatures below 200 K. The rate coefficients are greater for ∆ j =-2 transitions in comparison to other transitions. The collision rates and other dynamical attributes between He and the molecule computed at cold temperatures will lead to model its abundance in ISM. References 1. Roueff and F. Lique , Chem. Rev. , 2013, 113 , 8906-8938. 2. Ritika and T. J. Dhilip Kumar, Not. R. Astron. Soc., 2022, 515 , 5145-5150.
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