D. L. FIACCO, S. W. HUNT AND K. R. LEOPOLD, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.

We report the first microwave spectroscopic investigation of the 1:1 complex of H2O-H2SO4 and several of its deuterated and 18O containing isotopomers. The complex is prepared in situ via reaction of water and SO3 using a co-injection source in which H2O vapor is introduced into the early stages of an Ar + SO3 expansion. Both a- and c- type spectra for fourteen isotopomers have been measured and are consistent in all cases with that of a near-prolate rotor with appreciable dipole moment components along the a- and c- inertial axes. The spectra of the isotopomers containing H216O are complicated by internal motion of the water unit affecting both the a-type K-1 = 0 and several of the c-type transitions. The possible internal motions giving rise to the observed spectral splittings as well as the ground state structural parameters of the H2O-H2SO4 complex will be discussed and compared to recent DFT calculations.,