Rotational dynamics of CNCN by p-H₂ and o-H₂ collision at interstellar temperatures.

This article focuses on the theoretical study of the rotational collisional dynamics of isocyanogen (CNCN) with para- and ortho-hydrogen (p-H₂ and o-H₂) at temperatures relevant to cold dense molecular clouds in the interstellar medium. A four-dimensional (4D) potential energy surface (PES) for the CNCN–H₂ system was computed using high-level ab initio methods (CCSD(T)-F12b/AVTZ) and subsequently fitted with a neural network model to achieve spectroscopic accuracy. Using this PES, state-to-state rotational cross sections and rate coefficients were calculated via close-coupling and centrifugal sudden methods, revealing a propensity for even Δj transitions and higher collisional rates with o-H₂ compared to p-H₂. The study also compares CNCN–H₂ collisional rates with those of CNCN–He and NCCN–H₂, providing insights into molecular interactions important for interpreting interstellar nitrile chemistry.