Abundances of carbon-bearing diatomic molecules in diffuse interstellar clouds.

In order to test in detail theories concerning the gas-phase chemistry of light interstellar molecules, it is necessary to have a coherent body of observational data for a large number of sight lines. In the present investigation new and previously published data for 22 stellar lines of sight are combined to provide a basis for the study of the relative abundances of CO, CN, CH, and CH(+). New data include millimeter-wave observations of CO toward several stars in both the 2.6 and 1.3 mm rotational lines. It is found that CO column densities (deduced largely from radio data) correlate very well with those of CN (determined purely by optical means) in regions possessing measurable CN absorption features. This correlation extends over nearly two orders of magnitude in the column densities of both species.