Abstract:
Quantum dynamics of the molecule cyanogen (NCCN) and its collision with helium taking place
in the interstellar medium has been studied. An ab initio potential energy surface of NCCN−−He,
a van der Waals complex, is generated using the high-level single reference coupled-cluster with
single and double and perturbative triple excitation method and aug-cc-pVQZ basis sets. Using the
multipole expansion, Legendre coefficients have been calculated and utilized in determining collisional cross sections. Close-coupling calculations have been performed to study rotational excitations
for He collision with NCCN. Due to nuclear spin statistics, collision induced transitions have even
∆j, while odd ∆j transitions are forbidden. The presence of resonances arising from rapid oscillation of cross sections in the low energy region is the result of quasi-bound states in the NCCN−−He
van der Waals complex. Among all the transitions, ∆j = 2 are found to be predominant for excitation. Thereafter, for each transition, the rate coefficients have been calculated which decrease
with increasing values of j and ∆j. The result of this work will be helpful to accurately model the
abundance of cyanogen in stellar atmospheres and interstellar gas. Published by AIP Publishing.
