Various static spin-correlation functions and the weights of the spin
excitations, or collective normal modes, in the van Hove response func
tion, observed in neutron scattering experiments, are calculated as a
function of temperature for a model quantum-spin chain. The spins inte
ract through an isotropic Heisenberg exchange that extends to nearest-
neighbour spins. In our model, spins of magnitude 1/2 form a dimerized
chain with alternating exchange interactions. We explore the static a
nd dynamic properties for ferromagnetic and antiferromagnetic exchange
interactions. Results for the various properties are shown to be exac
t in the limit of a high temperature, and we argue that the results ar
e very good at low temperatures. Unlike the case for linear spin-wave
theory, the results are also exact in the limit of strong dimerization
, i.e. non-interacting coupled pairs of spins.