Probing the magnetic field with molecular ion spectra. II.

We present further observational evidence in support of our earlier proposa l for detecting the presence of the magnetic field in molecular clouds by c omparing spectra of molecular ions with those of neutral molecules. The ion lines tend to be narrower and do not show the wings due to flows, when the magnetic held is sufficiently strong. We obtained spectra for the opticall y thin lines of the (HCN)-C-13 and (HCO+)-C-13 species in a sample of 10 mo lecular clouds and found the results to be in agreement with our previous o bservations of the main isotopic species, HCN and HCO+, made in OMC-1, OMC- 2, OMC-3, and DR 21(OH), thus eliminating the possibility of optical depth effects playing a role in the ion line narrowing. HCS+ was also detected in four of these star-forming regions. We also discuss previously published r esults by Benson et al. of N2H+ detections in a large sample of dark clouds . We show that the similarity in line widths between ion and neutral specie s in their sample is consistent with the relatively small amount of turbule nce and other flows observed in these clouds.