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We present high spatial resolution infrared imaging and long slit spectra of the molecular shock in the supernova remnant IC443. The 1--0 S(1) line of H$_2$ at 2.122 $mu m$ has been imaged at an angular resolution of 0.7'' over an area of 50'' x 65'' in the vicinity of the peak emission near the southeast edge of the supernova remnant. At this resolution the shock excited H$_2$ emission breaks up into a wealth of structure, consisting of features with sizes ranging from 1'' up to scales extending beyond the edges of the image. Unlike the optical emission from supernova remnant shocks, the H$_2$ emission cannot be well described as a filamentary structure, but is better portrayed as a chaotic assemblage of knots.
Long slit spectra of the H$_2$ emission has been obtained to constrain the excitation conditions in the molecular gas. The data include 2, 3, and 4 $\mu$m lines from the 1--0, 2--1, 3--2 vibrational bands together with high-J pure rotational lines. The energy of the upper levels of these lines spans excitation energies from 7000 -- 25,000 K. These data enable us to determine the H$_2$ level population with great precision, for comparison with predictions of C-- and J--shock models, and to look for correlation between spatial variation of excitation and the H$_2$ surface brightness. The spectra show remarkably constant H$_2$ line ratios over the length of the slit (90''). Since C-shock models predict temperature variation on scale lengths comparable to the MHD damping length -- a few arc seconds at the distance of IC443 -- this result tends to suggest that a dissociative J--shock is preferred.
