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Nonpolar a-plane ZnO thin films are grown on LiGaO2 substrates and their optical and vibronic characteristics are investigated. Raman spectroscopy under nonresonant and resonant excitations shows the phase purity and resonant multiphonon process. From multiphonon Raman peaks up to the 6th order in the resonant spectra, the LO phonon frequencies for wave vectors away from the Γ point are estimated using the cascade model. Polar LO phonons with E1 symmetry play an important role in the indirect transitions of hot excitons. The optical anisotropy has been studied on the basis of polarization-dependent photoluminescence. The origin of photoluminescence is studied and a donor binding energy of 74.6 meV is found.