ROTATIONAL FREQUENCY-SHIFT

The notion of the rotational frequency shift, an analog of the Doppler shift, is introduced. This new frequency shift occurs for atomic syst ems that lack rotational invariance, but have stationary states in a r otating frame. The rotational frequency shift is given by the scalar p roduct of the angular velocity and the angular momentum of the emitted photon in full analogy with the standard Doppler shift which is given by the scalar product of the linear velocity of the source and the li near momentum of the photon. The rotational frequency shift can be obs erved only in a Mossbauer-like regime when the angular recoil is negli gible.