  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 C2+ 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 H2 density
begins to be significant. Populations that deviate strongly from the local
thermodynamic equilibrium are predicted for C2+ in environments where it may be
detectable. Consequences of this are discussed and a new optical spectrum is
calculated.
