On the rotational energy distributions of reactive, non-polar species in the interstellar medium

Abstract

A basic model for the formation of non-equilibrium rotational energy distributions is described for reactive, homo-polar diatomic molecules and ions in the interstellar medium. Kinetic models were constructed to calculate the rotational populations of C 2 + under the conditions it would experience in the diffuse interstellar medium. As the non-polar ion reacts with molecular hydrogen, but not atomic hydrogen, the thermalization of a hot nascent rotational population will be arrested by chemical reaction when the H 2 density begins to be significant. Populations that deviate strongly from the local thermodynamic equilibrium are predicted for C 2 + in environments where it may be detectable. Consequences of this are discussed and a new optical spectrum is calculated.