  Studying the dynamical spin structure factor in frustrated spin chains with
spontaneously dimerized ground state we show that besides the gapped spin-wave
excitations there appears at finite temperatures also a sharp central peak. The
latter can be attributed to deconfined spinons, accounted well within the
variational approach. The central peak remains well pronounced within the local
spin dynamics and may be relevant for experiments on materials with 1D
frustrated spin chains.
