Influence of spontaneous radiation on the precision of reproduction of the frequency of a molecular transition by nonlinear spectroscopy methods

An analysis is made of distortions of the profile of a recoil doublet due to the influence of spontaneous radiation considered in the transit limit. It is shown that in the case of a methane line (λ = 3.39 μ) these distortions shift the reproduced frequency from the center of a molecular transition line by about 1 Hz.