|VOLUME 94 (2011) | ISSUE 6 |
Propagating vibrational excitations in molecular chains
V. A. Benderskii∇, E. I. Kats
∇Institute of Problems of Chemical Physics RAS, 142432 Chernogolovka, Russia
Laue-Langevin Institute, F-38042 Grenoble, France
L.D. Landau Institute for Theoretical Physics, RAS, Moscow, Russia
We investigate quantum
dynamics of vibrational excitations in one-dimensional (1D) molecular chain.
Our model includes nearest neighbor
interaction between identical molecular sites and one impurity atom placed
in the middle (n=0). We show that upon
exciting the impurity site, its excess energy for relatively long for
molecular scales time up to 100 ps is not redistributed
uniformly among all other degrees of freedom. On the contrary an
excitation propagates along the chain, reflected from the chain ends,
and quantum interference of these waves yields to recurrence cycles and
echo phenomena. For a critical cycle number kc, echo components of
the neighboring cycles start to overlap, and
eventually for dynamics looks like chaotic one.
The critical cycle number kc depends on the coupling
strength of the impurity site with its neighbors .
kc achieves the maximum for C2 = 1/2.
Our results are in qualitative agreement with experimental data on
vibrational excitations in various (CH2)n molecular chains,
and besides offer a way for loss-free energy transfer
between separated in space reaction centers.