Knowledge Bank

The practical application of radio frequency-microwave double $resonance1$ (RFMDR) as a spectroscopic technique in the analysis of microwave spectra has been investigated. A high-power amplitude-modulated radio-frequency field applied to the Stark septum of a conventional waveguide provides a means of detecting microwave transitions, analogous to the situation in microwave-microwave double resonance (MMDR). The sensitivity of the technique compares favorably with that of MMDR and Stark modulation. Nearly prolate asymmetric top molecules with allowed a-type transitions are especially amenable to the technique due to the presence of favorable radio-frequency transitions between asymmetry doublets. Accidental near degeneracies of dipole-connected rotational levels are also useful. A description of a RFMDR spectrometer using conventional as well as slightly modified Stark cell waveguides will be presented. Limitations and special problems posed by the nature of radio-frequency circuits will be discussed, and examples of applications together with suggestions for other possible uses will be given.