  The region towards W51C is a convincing example of interaction between a
supernova remnant and a surrounding molecular cloud. Large electron abundances
have been reported towards the position W51C-E located in this interaction
region, and it was proposed that the enhanced ionization fraction was due to
cosmic ray particles freshly accelerated by the SNR shock. We present PdB
interferometer observations of the H$^{13}$CO$^+$(1-0) and DCO$^+$(2-1)
emission lines centered at position W51C-E. These observations confirm the
previous scenario of cosmic-ray induced ionization at this location. In
addition, SiO(2-1) emission has been successfully mapped in the close vicinity
of W51C-E, with a spatial resolution of 7". The morphology and kinematics of
the SiO emission are analyzed and strongly suggest that this emission is
produced by the passage of the SNR primary shock. Put in conjunction with the
enhanced ionization fraction in this region, we give a consistent picture in
which the W51C-E position is located downstream of the shock, where a large
reservoir of freshly accelerated particles is available.
