A quantum mechanical calculation of the CN radiative association

Radiative association of CN is investigated through the quantum mechanical method, including the cross sections and rate coefficients. The ab initio potential energy curves, transition dipole moments, and permanent dipole moments of CN are obtained by the internally contracted multireference configuration interaction method with Davidson correction and aug-cc-pwCV5Z-DK basis set. For the collision of the ground state C (P-3(g)) and N (S-4(u)) atoms, except for the four previously studied processes including the A(2)pi -> X-2 sigma(+), X-2 sigma(+) -> A(2)pi, A(2)pi -> A(2)pi, and X-2 sigma(+) -> X-2 sigma(+) transitions, four other radiative association processes including b(4)pi -> a(4)sigma(+), a(4)sigma(+) -> b(4)pi, b(4)pi -> b(4)pi, and a(4)sigma(+) -> a(4)sigma(+) transitions are considered. We also considered the collision of the excited C (D-1(g)) and the ground N (S-4(u)) atoms including the 2(4)pi -> 1(4)sigma(-) process and the collision of the ground C (P-3(g)) and the excited N (D-2(u)) atoms including 2(2)pi -> B-2 sigma(+), 3(2)pi -> B-2 sigma(+), and 4(2)pi -> B-2 sigma(+) transitions. The temperature population factor is considered to describe the thermal population of the three different dissociation asymptotic energies. The results show that the contribution of the A(2)pi -> X-2 sigma(+) and b(4)pi -> a(4)sigma(+) transitions to the total rate coefficients is significant over the entire temperature range. While considering the collision of C and N involving excited states, the contribution of the 2(2)pi -> B-2 sigma(+), 3(2)pi -> B-2 sigma(+), and 4(2)pi -> B-2 sigma(+) transitions to the total rate coefficients cannot be ignored at the temperature range larger than 10 000 K. Finally, the rate coefficients are fitted to an analytical function for astrochemical reaction modelling.