Contribution Invited Talk
Molecular Ions as Tracers of the Cosmic-Ray Ionization Rate
Cosmic rays play a vital role in initiating the chemistry that occurs in molecular clouds. The ionization of H and H$_2$ begins a network of ion-molecule reactions responsible for generating many of the diatomic and small polyatomic molecules observed in the interstellar medium. A few such species --- OH$^+$, H$_2$O$^+$, and H$_3^+$ in particular --- are formed and destroyed by rather simple processes, making them powerful probes of the cosmic-ray ionization rate. I will discuss the current status of observations of these molecular ions within our Galaxy, as well as the conclusions that can be drawn from this ever-growing sample.