  We have measured far infrared reflectance and transmittance spectra as well
as Raman scattering spectra of \alpha'-NaV2O5 single crystals for all the
principal polarizations. The temperature range above the phase transition
temperature T_c=35 K was investigated, mainly. On the basis of this
experimental study and of the lattice dynamics calculations we conclude that
the symmetry of NaV2O5 in the high temperature phase is described by the
centrosymmetric D_{2h}^{13} space group. The assignment of the observed phonons
is given. Values of dielectric constants are obtained from the infrared data.
Asymmetric shapes of several infrared lines as well as higher order infrared
vibrational spectra are discussed. The crystal field energy levels of the 3d
electron localized at the V^{4+} site have been calculated in the framework of
the exchange charge model using the values of effective charges obtained from
the lattice dynamics calculations. According to the results of these
calculations, the earlier observed broad optical bands in the region of 1 eV
can be interpreted as phonon assisted d-d transitions.
