  Inelastic neutron scattering experiments on Nd2BaNiO5 single-crystals and
powder samples are used to study the dynamic coupling of 1-dimensional
Haldane-gap excitations in the S=1 Ni2+ -chains to local crystal-field
transitions, associated with the rare earth ions. Substantial interference
between the two types of excitations is observed even in the 1-dimensional
paramagnetic phase. Despite that, the results provide solid justification for
the previously proposed ``static staggered field'' model for R2BaNiO5
nickelates. The observed behaviour is qualitatively explained by a simple
chain-Random-Phase-Approximation (chain-RPA) model.
