C+ and the connection between different tracers of the diffuse interstellar medium

Using radio, microwave, sub-mm, and optical data, we analyze several lines of sight toward stars generally closer than 1 kpc on a component by component basis. We derive the component structure seen in emission from C$^{+}$, H I, and CO and its isotopoloques, along with those for CH$^{+}$, CH, CN, Ca II, and Ca I in absorption. We study how these tracers are related to the CO-Dark H$_{2}$ gas being probed by C$^{+}$ emission and discuss the kinematic connections among the species. Physical conditions of the various components seen in absorption, especially density, are inferred from a simple chemical analysis based on the column densities of CH$^{+}$, CH, and CN