MICROWAVE SPECTRA OF THE FURAN-$SO_{2}$ COMPLEX

Author Institution: Jet Propulsion Laboratory; Department of Chemistry, University of MichiganThe microwave spectrum of the furan-sulfur dioxide complex has been observed with a pulsed molecular beam Fourier transform microwave spectrometer. Transitions having a-, b- and c- dipole selection rules were all seen. The rotational constants are $A=3190$.7285(11). $B=1119.3596(2)$, and $C=1015.6841(2) MHz$. In addition the rotational spectra of the $C_{4}H_{4}O-^{34}SO_{2}$, $C_{4}H_{4}O^{18}O_{2}$, $C_{4}D_{4}O$, $SO_{2}$, and two different $C_{4}H_{4}O$ $\cdot$ $SO^{18}O$, isotopic species were assigned. The two monomers are separated by 3.43(1) \AA $(R_{cm}$), with the $SO_{2}$ lying above the furan plane. The two $C_{2}$ axes of the monomer units are skewed by about $65^{\circ}$ and the plane of the $SO_{2}$ is tipped considerably from parallel to the furan plane, with the sulfur atom closest to the furan. While one oxygen in $SO_{2}$ lies approximately above the oxygen of the furan, the other is located closer to a $\beta$-carbon of the furan. Splittings of the c-dipole transitions for various isotopes suggest a tunneling motion between two equivalent forms of the complex