2001A&A...376L...5K

We present the first detection of the nu ro-vibrational band of gas-phase SO₂ in absorption in the mid-infrared spectral region around 7.3µm of a sample of deeply embedded massive protostars. Comparison with model spectra shows that the derived excitation temperatures correlate with previous C₂H₂ and HCN studies, indicating that the same warm gas component is probed. The SO₂ column densities are similar along all lines of sight suggesting that the SO₂ formation has saturated, but not destroyed, and the absolute abundances of SO₂ are high (∼10^–7). Both the high temperature and the high abundance of the detected SO₂ are not easily explained by standard hot core chemistry models. Likewise, indicators of shock induced chemistry are lacking.