C-TYPE SHOCKS IN THE INTERSTELLAR-MEDIUM - PROFILES OF CH-LINES( AND CH ABSORPTION)

We have computed optical absorption-line profiles of CH+ and CH, as pr edicted by a model of a C-type shock propagating in a diffuse interste llar cloud. Both these species are produced in the shock wave in the r eaction sequence that is initiated by C+(H-2, H)CH+. Whilst CH+ flows at the ion speed, CH, which farms in the dissociative recombination re action CH3+(e(-), H-2)CH, flows at a speed which is intermediate betwe en these of the ions and the neutrals. The predicted velocity shift be tween the CH+ and CH line profiles is found to be no more than approxi mately 2 km s(-1), which is smaller than has previously been assumed. We also investigate OH and HCO+, finding that the correlation between their column densities, recently observed in the diffuse interstellar medium, can be reproduced by the model.