MICROWAVE SPECTRA OF THE $K=1\leftarrow 0$ ROTATION-TUNNELING BANDS OF ($D_{2}O)_{2}$ AND HOD--$D_{2}O$

Abstract

A 78-118 GHz frequency synthesizer based on a backward-wave-oscillator (BWO) microwave source has been used with an electric-resonance optothermal spectrometer to record the microwave spectra of the $K=1\leftarrow 0$ rotation-tunneling subbands of ($D_{2}O){2}$ and $HOD-D{2} O$. For $(D_{2} O){2}$, two such bands are observed, one for the $A{1}^\pm$, $E_{1}^\pm$, and $B_{1}^\pm$ states near 155 GHz and one for the $A_{2}^\pm$ $E_{2}^\pm$, and $B_{2}^\pm$ states near 84 GHz. Two bands are also observed for HOD-DOD, each split by a tunneling motion that interchanges two deuterium nuclei, as inferred from the 2:1 intensity ratio observed for the transitions of the two tunneling components. The origins for the two HOD-DOD bands are at 112 GHz and 69 GHz. The present results when combined with previous measurements of us and others for the $\Delta K=0$, $K=0$ and 1 bands and the $K=2\leftarrow$1 bands allows an essentially complete characterization of the rotation-tunneling states of ($D_{2}O)_{2}$ up to $K=2$.""