We present the results of computations of both one-fluid hydro-dynamic and three-fluid magnetohydrodynamic models of interstellar molecular shocks. A network of over 150 chemical reactions was incorporated in the models with a view to correctly predicting the variation of the fractional ionization in the precursors of MHD shocks and the column densities of a number of chemical species, particularly CH+, which may be selectively formed in shocks. We find that one-fluid hydrodynamic models predict column densities of CH+ which are too small to be considered compatible with observations. The MHD models are more successful in this respect, CH+ being formed by the endothermic C+(H2,H) CH+ reaction, driven by ambipolar diffusion. However, difficulties remain in simultaneously reproducing the observed column densities of other species which are formed in shocks, specifically the excited rotational states of H2.
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Forêts et al. (1986) studied this question.