We study the spectrum of electromagnetic waves emitted by oscillator, trapped in an external potential well. It is
assumed that the natural frequency of the oscillator is much greater than the frequency of oscillations in the potential
well. We consider the quantum model of emission with taking into account the recoil effect. The highest intensity of
the absorption and emission lines is observed on the eigenfrequency of the oscillator when the recoil energy is equal
to energy of the quantum of low-frequency oscillations in the potential well.
