Gas-phase SO2 in absorption towards massive protostars

We present the first detection of the v(3) ro-vibrational band of gas-phase SO2 in absorption in the mid-infrared spectral region around 7.3 mum of a sample of deeply embedded massive protostars. Comparison with model spectra shows that the derived excitation temperatures correlate with previous C2H 2 and HCN studies, indicating that the same warm gas component is probed. T he SO2 column densities are similar along all lines of sight suggesting tha t the SO2 formation has saturated, but not destroyed, and the absolute abun dances of SO2 are high (similar to 10(7)). Both the high temperature and th e high abundance of the detected SO2 are not easily explained by standard h ot core chemistry models. Likewise, indicators of shock induced chemistry a re lacking.