Synthesis of interstellar CH + without OH

Abstract

Both CH+ and OH can be produced in warm gas via endothermic reactions, yet recent observations by Federman, Weber & Lambert indicate little correspondence between the abundances for these molecules. A non-thermal origin for CH+ production is therefore suggested. Chemical models of diffuse cloud envelopes that include the presence of Alfvén waves are shown to be consistent with the new observations. In these models, CH+ is formed as a result of the streaming of C+ ions, which are influenced by the passage of Alfvén waves, relative to the cold background gas. Since the background gas is cold, OH production arises solely from ion-molecule reactions initiated by cosmic ray ionization.