Probing the magnetic field with molecular ion spectra

Observations of the effect of the magnetic held on its environment are usua lly achieved with techniques that rely on its interaction with the spin of the particles under study. Because of the relative weakness of this effect, extraction of the held characteristics proves to be a most challenging tas k. We take a totally different approach to the problem and show that the ma nifestation of the magnetic held can be directly observed by means of a com parison of the spectra of molecular ions with those of neutral molecules. T his takes advantage of the strong cyclotron interaction between the ions an d the held, but requires the presence of flows or turbulent motion in the g as. We compare our theory to data obtained on the OMC-1, OMC-2, OMC-3, and DR 21(OH) molecular clouds.