  Detailed far-infrared spectra of the optical phonons are reported for
antiferromagnetic MnO. Eigenfrequencies, phonon damping and effective plasma
frequencies are studied as a function of temperature. Special attention is paid
to the phonon splitting at the antiferromagnetic phase transition. The results
are compared to recent experimental and theoretical studies of the spin-phonon
coupling in frustrated magnets, which are explained in terms of a spin-driven
Jahn-Teller effect, and to ab initio and model calculations, which predict
phonon splitting induced by magnetic order.
