The CN radical in diffuse interstellar clouds

A survey of 15 lines of sight for the CN B2Sigma(+) X2Sigma(+) interstellar absorption lines shows that the CN column density in diffuse interstellar clouds follows the relation log N(CN) is proportional to m log N(H2), where m is approximately equal to 3. This result is reproduced by a reaction network in which CN is produced primarily from C2 by the neutral-neutral reaction C2 + N yields CN + C, and photodissociation is the main destruction pathway for the neutral molecules CH, C2, and CN. The CN radical is the first molecular species observed in diffuse clouds that requires a neutral-neutral reaction for its formation in the gas phase. The network also reproduces the observed ratio N(CN)/N(H2).