SiO production in interstellar shocks

We study the production of SiO in the gas phase of molecular outflows, through the sputtering of Si-bearing material in grains. The sputtering is driven by neutral particle impact on charged grains in C-type shocks, at the speed corresponding to ambipolar diffusion. Shock speeds in the range 10 < vs < 40 km s−1 and preshock densities 104 < nH < 107cm−3 have been investigated. Sputtering of Si-bearing material in both the cores and the mantles of the grains is considered. We find that, for vs of approximately 25 km s−1 and nH of the order 105 cm−3, column densities of SiO similar to those observed in molecular outflow regions can be generated by either mechanism. Impact by particles heavier than helium dominates the core-sputtering process for shock velocities of this order. The profiles of rotational transitions of SiO are computed and compared with observations of molecular outflows.