  We report inelastic electron tunneling spectroscopy (IETS) of multilayer
molecular junctions with and without incorporated metal nano-particles. The
incorporation of metal nanoparticles into our devices leads to enhanced IET
intensity and a modified line-shape for some vibrational modes. The enhancement
and line-shape modification are both the result of a low lying hybrid metal
nanoparticle-molecule electronic level. These observations explain the apparent
discrepancy between earlier IETS measurements of alkane thiolate junctions by
Kushmerick \emph{et al.} [Nano Lett. \textbf{4}, 639 (2004)] and Wang \emph{et
al.} [Nano Lett. \textbf{4}, 643 (2004)].
