SWS SPECTROSCOPY OF THE COLLIDING GALAXIES NGC-4038 39/

We present mid-infrared spectroscopy of the prototypical interacting g alaxies NGC 4038/39 (the 'Antennae') obtained with the ISO Short Wavel ength Spectrometer (SWS). Our observations focus on the interaction zo ne where the two galaxies overlap, providing new constraints on the pr operties of the young and vigorous extranuclear starburst triggered by the recent interaction of the two galaxies. We use hydrogen recombina tion lines to derive an extinction of A(v) approximate to 70 to the st arburst region, concluding that a model where emitting gas and absorbi ng dust are mixed best fits the data. We discuss the use of mid-infrar ed fine structure line ratios for determining the average effective te mperature of the stellar ionizing radiation field, and derive an avera ge temperature of 44000 K from the extinction-corrected [NeIII]15.6 mu m/[NeII]12.8 mu m line ratio. The observations are well described by starburst models for a recent starburst with an initial mass function extending up to 100 Mg.. Observations of the pure rotational (0-0) S(1 ) and S(2) lines of molecular hydrogen are used to constrain the fract ion of molecular gas that is at temperatures of a few hundred Kelvin.