Isotope effect on the formation of CN by radiative association reactions

Abstract

The formation of CN and its isotopologue C15N through radiative association has been investigated. We considered two processes for the collisions of ground state C(3P) and N(4S) atoms (A2Π → X2Σ+ and b4Π → a4Σ+), as well as, for the first time, we investigated the radiative association of ground state C(3P) and excited N(2D) atoms (B2Σ+ → X2Σ+). The cross-sections for the three processes have been calculated using semi-classical, quantum mechanical, and Breit–Wigner theories. The rate constants, derived from the combination of semi-classical and Breit–Wigner results, have been fitted to the Kooij formula to be used in astrochemical modeling. The rate constant for the B2Σ+ → X2Σ+ process dominates in the investigated temperature range (10–10 000 K), when its own asymptotic energy is used as a reference level. Moreover, the B2Σ+ → X2Σ+ process presents the most pronounced isotope effect on the rate constant. We suggest considering these newly investigated radiative association processes for the formation of CN and C15N in the interstellar medium.