Electronic structure calculations and quantum dynamics of rotational deexcitation of CNNC by He

The quantum dynamics of rotational transitions of the diisocyanogen (CNNC) molecule undergoing collision with the helium (He) atom occurring in the interstellar medium (ISM) has been studied. The rotational deexcitation cross sections are extracted by first computing an ab initio potential energy surface of CNNC-He using the coupled-cluster with single and double and perturbative triple excitations with the F12a method (CCSD(T)-F12a) employing the aug-cc-pVTZ basis set. Utilizing the multipole expansions, collisional cross sections are determined for total energies of up to 1000 cm(-1) by the close coupling equations. The discussion on propensity rules suggests that the transitions have even Delta j values, while odd Delta j valued transitions are forbidden due to C and N nuclei spin statistics. Quasi-bound states present in the CNNC-He van der Waals complex resulted in the resonances coming from the rapid oscillations in the values of the cross sections in the region of low energy. Rotational deexcitation rate coefficients are further worked out by averaging the calculated cross sections at temperatures below 200 K. The new findings of the study will be beneficial in modeling the abundance of diisocyanogen in the ISM.

Automated summary

This study investigates the quantum dynamics of rotational transitions of the diisocyanogen molecule colliding with helium atom in the interstellar medium. By computing potential energy surface and extracting rotational deexcitation cross sections, the research reveals resonances in low energy region and calculates rotational deexcitation rate coefficients. The findings will be valuable for modeling the abundance of diisocyanogen in ISM.