  We investigate quantum tunneling in a translation invariant chain of
particles. The particles interact harmonically with their nearest neighbors,
except for one bond, which is anharmonic. It is described by a symmetric double
well potential. In the first step, we show how the anharmonic coordinate can be
separated from the normal modes. This yields a Lagrangian which has been used
to study quantum dissipation. Elimination of the normal modes leads to a
nonlocal action of Caldeira-Leggett type. If the anharmonic bond defect is in
the bulk, one arrives at Ohmic damping, i.e. there is a transition of a
delocalized bond state to a localized one if the elastic constant exceeds a
critical value $C_{crit}$. The latter depends on the masses of the bond defect.
Superohmic damping occurs if the bond defect is in the site $M$ at a finite
distance from one of the chain ends. If the observation time $T$ is smaller
than a characteristic time $\tau_M \sim M$, depending on the location M of the
defect, the behavior is similar to the bulk situation. However, for $T \gg
\tau_M$ tunneling is never suppressed.
