TUNNELING - ROTATIONAL SPECTRUM AND STRUCTURE OF $(H_{2}CO)_{2}$

Author Institution: Molecular Spectroscopy Division, National Institute of Standards and Technology; Department of Chemistry, Wesleyan University; Department of Chemistry, University of WashingtonThe microwave spectra of $(H_{2}CO)_{2}$ and $(D_{2}CO)_{2}$ have been observed with a pulsed beam, Fabry-Perot cavity, Fourier transform microwave spectrometer. Both species exhibit a- type spectra which are split by tunneling motions involving internal rotation of each monomer unit and an interchange motion of donor-acceptor, analagous to motions in the water dimer. Rotational analysis of the $(H_{2}CO)_{2}$ species provides the constants $A = 18583.(54) MHz, 4(B + C) = 3272.105(34) MHz$, and $B - C = 503.92(17) MHz$. Stark effect measurements on this species yield dipole moment components $\mu_{a} = 0.858(4) D$ and $\mu_{b} = 0.027(10) D$, and similiar values are obtained for $(D_{2}CO)_{2}$. The small value for $\mu_{b}$, has hampered observation of the expected b- type transitions. The structure obtained from fitting the moments of inertia has the planes of the monomer units perpendicular in a nearly antiparallel orientation of the CO groups and the center-of-mass separation is 3.046(17) {\AA}. Comparison of these results with other complexes containing $H_{2}CO$ will be presented