  Exact diagonalization calculations of finite antiferromagnetic spin-1
Heisenberg chains at finite temperatures are presented and compared to a recent
inelastic neutron scattering experiment for temperatures T up to 7.5 times the
intrachain exchange constant J. The calculations show that the excitations at
the antiferromagnetic point q=1 and at q=0.5 remain resonant up to at least
T=2J, confirming the recent experimental observation of resonant
high-temperature domain wall excitations. The predicted first and second
moments are in good agreement with experiment, except at temperatures where
three-dimensional spin correlations are most important. The ratio of the
structure factors at q=1 and at q=0.5 is well predicted for the paramagnetic
infinite-temperature limit. For T=2J, however, we found that the experimentally
observed intensity is considerably less than predicted. This suggests that
domain wall excitations on different chains interact up to temperatures of the
order of the spin band width.
