Measurements of CH and CH/+/ in diffuse interstellar clouds

A survey of CH and CH(+) absorption was made for directions with known amounts of atomic and molecular hydrogen. Both radicals are detected only toward directions with substantial amounts of H2 (H2 density greater than about 10 to the 18th/sq cm). The column density of CH varies linearly with H2 density; CH(+) density is independent of H2 density. The CH line is shifted in velocity from CH(+) line in approximately 50% of the lines of sight. A model which incorporates the presence of a shock best describes the chemical and the dynamical information available from the data.