Rotational (de-)excitation of isocyanogen by collision with helium at low energies.

Isocyanogen, CNCN, was discovered very recently in the interstellar medium (ISM). At present, the rate coefficients for the rotational (de-)excitation of CNCN by collisions with He are determined. First, we mapped the interaction potential between CNCN and He in Jacobi coordinates using highly correlated ab initio methodology. Then, an analytical expansion of the CNCN-He potential energy surface is derived. Later on, quantum dynamical treatments of nuclear motions are performed using the close coupling technique. We obtained the cross sections for the rotational (de-)excitation of CNCN after a collision by He up to 2000 cm-1 total energies. These cross sections are used to deduce the collision rates in the 10-300 K range. These data are needed for modeling the CNCN abundances in the ISM. This work should help for determining the abundance of such non-symmetrical dicyanopolyynes in astrophysical media and indirectly the symmetric one [Cyanogen (NCCN)].