THE FORMATION OF CN AND CN' BY DIRECT RADIATIVE ASSOCIATION

Rate coefficients for direct radiative association of carbon and nitrogen atoms to form CN, and of carbon ions and nitrogen atoms to form CN + ions, are calculated for temperatures in the range of 300 to 14,700 K. For the CN molecule, the rate coefficients can be represented by the standard expression, kCN(T) = 7.87 × 10-19(T/300)0.056 exp(-96.0/T) cm3 s-1 for temperatures between 300 and 2700 K and kCN(T) = 1.37 × 10-18(T/300)-0.128 exp(-520.1/T) cm-3 s-1 at T > 2700 K. For the CN+ ion, the corresponding expression is k(T) = 1.08 × 10-18(T/300)0.071 exp(-57.5/T) cm-3 s-1 for the temperature range studied. Calculated rate coefficients kCN are about 2 orders of magnitude lower than the canonical value used in the modeling of the chemistry of various astrophysical environments.