Warm molecular hydrogen and ionized neon in the HH 2 outflow

We report on spectro-imaging observations of the Herbig-Haro 2 outflow with the ISOCAM camera on board the Infrared Space Observatory. The [Ne II] 12.81 mum and [Ne III] 15.55 mum lines are detected only toward the jet working surface (HH 2H), consistent with the high excitation of this knot in the optical range, while H-2 pure rotational emission is found all over the shocked region HH 2. The low-energy transition S(2) traces warm gas (T similar to 400 K) peaked toward knots E and F and extended ejecta (T similar to 250-380 K) with masses of a few times 10(-3) M. in the high-velocity CO outflow extending between the powering source and HH 2. Such emission M, could arise from low-velocity C-type shocks (v similar or equal to 10-15 km s(-1)). The higher transitions S(3)-S(7) trace the emission of hot shocked gas (T = 1000-1400 K) from individual optical knots in the HH 2 region. The ortho -to-para (OTP) ratio exhibits large spatial variations between 1.2 (knot E) and 2.5 (knot H), well below its value at LTE. The emission of the S(3) - S(7) lines is well accounted for by planar C-shock models with a typical velocity V-s = 20-30 km s(-1) propagating into a medium of density n(t) = 10(4)-10(5) cm(-3) with an initial OTP ratio close to 1 in the preshock gas. In the leading edge of the jet, where the geometry of the emission allows a simple modeling, a good agreement is found with velocities derived from the optical proper motions measured in the ionized gas.