Formation of Si-2, C-2, C-2(+) and N-2(+) by radiative association

Rate coefficients for the direct radiative association of silicon atoms to form Si-2, carbon atoms to form C-2, a carbon atom and a carbon ion to form the C-2(+) ion, and a nitrogen atom and a nitrogen ion to form the N-2(+) ion are estimated for temperatures in the range 300 to 14 700 K. For Si-2, the rate coefficients (k(Si2)) increase with an increase of temperature, and they can be expressed by k(Si2) = 2.19 x 10(-18) (T/300)(0.045) exp (- 258.79/T) cm(3) s(-1). At T greater than or equal to 7100 K, the rate coefficient k(Si2) is approximate to 2.5 x 10(-18) cm(3) s(-1) and is independent of temperature. The rate coefficients for C-2, C-2(+) and N-2(+) in the temperature range 300 to 14 700 K are fitted to the relation k = alpha (T/300)(beta) exp (- gamma/T) cm(3) s(-1), where alpha, beta and gamma are: 4.36 x 10(-18) cm(3) s(-1), 0.35 and 161.31 for C-2, 4.01 x 10(-18) cm(3) s(-1), 0.17 and 101.52 for the C-2(+) ion, and 3.71 x 10(-18) cm(3) s(-1), 0.24 and 26.12 for the N-2(+) ion, respectively. In each case, the rate coefficients increase with an increase of temperature.