Beam maser double resonance measurements on HDO

High resolution measurements of hyperfine structure on the 2 ₂₀-2₂₁ transition of HDO were made with a two-cavity beam maser using the Ramsey method and using a new double resonance technique. Resonances for magnetic dipole transitions between hyperfine sublevels of the rotational states were detected by observing intensity changes in the two-cavity interference pattern for microwave rotational transitions. The linewidth (fwhm) for the magnetic dipole transitions was 1 kHz. This linewidth allows better effective resolution than the two-cavity Ramsey resonance when nozzle beams are used. Deuterium quadrupole coupling and spin-rotation interaction strengths were obtained. This double resonance technique should be useful for other small molecules, particularly for those cases where the data cannot be obtained from the microwave transitions.