  We report on the detection of HCO+ and 12CO emission in the rotational
transition J=1-0 in the vicinity of the shock front at the southern border of
the supernova remnant RCW 103, where previous infrared observations suggest an
interaction with a molecular cloud. The observations were carried out with the
Australian Millimeter Radiotelescope at Mopra. We observed a depletion of HCO+
behind the supernova shock front. In addition, we studied the interstellar
medium over an extended region towards RCW 103 based on archival 21 cm HI line
observations from the Australia Telescope Compact Array (ATCA) and the Parkes
Telescope. No atomic gas is observed in emission in coincidence with the
molecular feature. This absence is interpreted in terms of self absorption
processes.
