  The spin dynamics of the prototypical quasi one-dimensional antiferromagnetic
Heisenberg spin S=1/2 chain KCuF3 is investigated by electron spin resonance
spectroscopy. Our analysis shows that the peculiarities of the spin dynamics
require a new dynamical form of the antisymmetric anisotropic spin-spin
interaction. This dynamical Dzyaloshinsky-Moriya interaction is related to
strong oscillations of the bridging fuorine ions perpendicular to the
crystallographic c axis. This new mechanism allows to resolve consistently the
controversies in observation of the magnetic and structural properties of this
orbitally ordered perovskite compound.
