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Aannestad, P.A., 1973: Molecule formation. II. In interstellar shock waves. Astrophys. J. Supp. Series, 25, 223-252, doi:10.1086/190268.
We study the processes of grain destruction and molecule formation due to the sputtering of grain mantles as the grains move relative to the gas in the hot shock wave. It is found that mantles are destroyed completely by this process if the abundance of molecular hydrogen is about 1 percent or more; the corresponding lifetime of a mantle is about 5×l07 years. We follow the variation of the molecular species through the shock wave using the sputtering process as a source for H2O, NH3, and CH4. It is found that OH and H20 may attain an abundance ~ 10-5 relative to H, but only over a narrow region about 10-3 pc immediately behind the shock front. For clouds of 200-500 M☉ the column densities are about 1013 cm-2 for OH and l012 cm-2 for H2O. The molecules CO, CN, and CH are found to be very abundant (10-4 to 10-6 relative to H) in the cold (~10°K) and dense (~104 to 105 cm-3) region far behind the shock front. Column densities are 1013 to 1014 cm-2 through the shock wave, but will increase by at least an order of magnitude as the wave travels through a cloud.
We study the cooling processes in the shock, including the effect of OH and H2O. It is found that cooling by molecules other than H2 is not important, except for CO, which may be the main cooling agent in the cold and dense region. We treat cooling by both ortho- and para-H2, and it is found that the 6.9-μ. (J = 7→5) transition of ortho-H2 gives the strongest H2 line for a wide range of shock velocities. For shock velocities greater than about 15 km/s, we find that collisional dissociation of H2 decreases the strength of the rotational lines substantially.
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