Principal chiral model scattering and the alternating quantum spin chain

We consider the critical alternating quantum spin chain with ${q_{+}\over 2}$, ${q_{-} \over2}$ spins. Using the Bethe ansatz technique we find explicit expressions for the $S$-matrix of the model. We show that in the limit that $q_{\pm} \rightarrow \infty$ our results coincide with the ones obtained for the principal chiral model level one, for the LL (RR) LR scattering. We also study the scattering of the bound states of the model and we recover the results of the XXZ (sine -Gordon) model.