Doppler effect for bound nuclear motion and its manifestation in resonant photoemission of oriented systems

In contrast to the common notion that Doppler effects have relevance only for atoms or molecules in free motion, we show that such effects should clearly be observable - and accounted for - in resonant scattering also when the nuclei are in bound state quantized motion. This untrivial effect does not influence the position of single resonances but only the center of gravity of the spectra. It is found to strongly depend on the duration time of the scattering.