  Here we study the relaxation of a chain consisting of 3 masses joined by
non-linear springs and periodic conditions when the stiffness is weakened. This
system, when expressed in their normal coordinates, yields a softened
Henon-Heiles system. By reducing the stiffness of one low-frequency vibrational
mode, a faster relaxation is enabeled. This is due to a reduction of the energy
barrier heights along the softened normal mode as well as for a widening of the
opening channels of the energy landscape in configurational space. The
relaxation is for the most part exponential, and can be explained by a simple
flux equation. Yet, for some initial conditions the relaxation follows as a
power law and, and in many cases, there is a regime change from exponential to
power law decay. We pin point the initial conditions for the power law decay,
finding two regions of sticky states. For such states, quasiperiodic orbits are
found since almost for all components of the initial momentum orientation, the
system is trapped inside two pockets of configurational space. The softened
Henon- Heiles model presented here is intended as the simplest model in order
to understand the interplay of rigidity, non-linear interactions and relaxation
for non-equilibrium systems like glass-forming melts or soft-matter.
