The influence of an off-resonant pump radiation in Fourier transform microwave spectroscopy

The influence of an off-resonant pump radiation during the free induction decay in Fourier transform microwave spectroscopy is analyzed. Applying the density-matrix formalism to a three-level system, it is shown that under special conditions a single line in the frequency domain splits into four lines and that the well-known symmetric coherence splitting is included for a resonant pump in this theory. Experimental results obtained with a microwave-microwave double-resonance spectrometer employing crossed Fabry-Perot cavities are also reported. All measurements on 1,2-difluorobenzene are in good agreement with the applied theory. (author)