  We investigate the electron spin resonance of the organic spin-Peierls chain
(o-DMTTF)2X with X = Cl, Br and I. We describe the temperature dependence of
the spin gap during the phase transition and quantify the dimerization
parameter $\delta$. At the lowest temperatures, the susceptibility is governed
by defects in the spin dimerized chain. Such strongly correlated defects are
the consequence of breaks in the translational symmetry of the chain. In the
vicinity of the defects the spins are polarized antiferomagnetically forming a
magnetic soliton: a spin 1 2 quasi-particle of size ruled by $\delta$ pinned to
the defects. For (o-DMTTF)2Br and (o-DMTTF)2Cl, we show that the one-half of
the total number of solitons are in isolation (as singles) whereas the other
half form pairs (soliton dimers)with a strong magnetic coupling. The Rabi
oscillations of both the single-soliton and the soliton-dimer are observed,
which is a prerequisite in the context of quantum information.
