Low Frequency Carbon Radio Recombination Lines II: The Diffuse
  Interstellar Medium
  In the second paper of the series, we have modeled low frequency carbon radio
recombination lines (CRRL) from the interstellar medium. Anticipating the LOw
Frequency ARray (LOFAR) survey of Galactic CRRLs, we focus our study on the
physical conditions of the diffuse cold neutral medium (CNM). We have used the
improved departure coefficients computed in the first paper of the series to
calculate line-to-continuum ratios. The results show that the line width and
integrated optical depths of CRRL are sensitive probes of the electron density,
gas temperature, and the emission measure of the cloud. Furthermore, the ratio
of CRRL to the [CII] at 158 $\mu$m line is a strong function of the temperature
and density of diffuse clouds. Guided by our calculations, we analyze CRRL
observations and illustrate their use with data from the literature.
