  Galactic supernova remnants (SNRs) and their environments provide the nearest
laboratories to study SN feedback. We performed molecular observations toward
SNR W49B, the most luminous Galactic SNR in the X-ray band, aiming to explore
signs of multiple feedback channels of SNRs on nearby molecular clouds (MCs).
We found very broad HCO+ lines with widths of dv = 48--75 km/s in the SNR
southwest, providing strong evidence that W49B is perturbing MCs at a systemic
velocity of $V_{LSR}=61$--65 km/s, and placing W49B at a distance of $7.9\pm
0.6$ kpc. We observed unusually high-intensity ratios of HCO+ J=1-0/CO J=1-0
not only at shocked regions ($1.1\pm 0.4$ and $0.70\pm 0.16$), but also in
quiescent clouds over 1 pc away from the SNR's eastern boundary (> 0.2). By
comparing with the magnetohydrodynamics shock models, we interpret that the
high ratio in the broad-line regions can result from a cosmic-ray (CR) induced
chemistry in shocked MCs, where the CR ionization rate is enhanced to around
10--100 times of the Galactic level. The high HCO+/CO ratio outside the SNR is
probably caused by the radiation precursor, while the luminous X-ray emission
of W49B can explain a few properties in this region. The above results provide
observational evidence that SNRs can strongly influence the molecular chemistry
in and outside the shock boundary via their shocks, CRs, and radiation. We
propose that the HCO+/CO ratio is a potentially useful tool to probe an SNR's
multichannel influence on MCs.
