BELL-SHAPE SOLITON PAIR IN A HYDROGEN-BONDED CHAIN WITH ASYMMETRIC DOUBLE-WELL POTENTIAL

In a hydrogen-bonded molecular chain with an asymmetric double-well potential, the nonlinear excitation is a slow-mode bell-shape soliton-antisoliton pair corresponding to two parallel electric dipoles or a fast-mode bell-shape soliton-soliton pair corresponding to two antiparallel electric dipoles. The soliton pair, propagating in a spatially inhomogeneous chain, may transform from a slow-mode soliton-antisoliton pair into a fast-mode soliton-soliton pair. This means that a reversion of the electric dipole in one of the two sublattices will occur. When the soliton pair propagates in a repulsion-type impurity region, there is a critical velocity nu(cr): if the velocity of the incident soliton pair nu equals nu(cr), its trajectory in phase space will branch. The incident soliton pair with velocity nu>nu(cr) can pass through the impurity region. Thus, for an incident soliton pair with velocity nu<nu(cr) there exist forbidden regions.