  We performed inelastic neutron scattering measurements on a polycrystalline
sample of a classical kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$ to
investigate the possibility of a dispersionless zero-energy excitation
associated with rotation of spins along the chains. The observed spectra indeed
exhibit such an excitation with strong intensity at low energy, as well as
dispersive excitations with weak intensity at high energy. Combining the
measurements with calculations from linear spin-wave theory reveals that
NaBa$_{2}$Mn$_{3}$F$_{11}$ is a good realization of the classical kagome
antiferromagnet which exhibits a dispersionless mode lifted by the magnetic
dipole-dipole interaction.
