HYDROGEN BOND NETWORK ISOMERS OF THE WATER NONAMER AND DECAMER OBSERVED BY BROADBAND ROTATIONAL SPECTROSCOPY

Author Institution: Department of Chemistry, University of Virginia, McCormick Rd.; Charlottesville, VA 22904-4319; Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warszawa, Poland; Dean's Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University, Lewisburg, PA 17837After our previous study of the rotational spectrum of water clusters in the 6-18 GHz region, in order to study clusters of larger size ($>$8 water molecules), a chirped-pulse Fourier transform microwave spectrometer in the 2-8 GHz frequency range has been used to obtain the broadband rotational spectra of five water nonamer isomers and four water decamer isomers in a pulsed molecular beam. The oxygen atom framework geometries for three nonamers and two decamers have also been unambiguously identified from isotopic labeling measurements using an H$_{2}$$^{18}$O enriched sample. Three of the four observed water decamer show tunneling effect associated with the internal dynamics of hydrogen-bond network in a similar fashion as the prism water hexamer. These tunneling paths are quenched upon a single incorporation of a H$_{2}$$^{18}$O molecule in the cluster. Due the large amount of closely-spaced rotational transitions in the H$_{2}$$^{18}$O spectrum, automated fitting tools were employed to extract the corresponding rotational spectra, which will be also briefly described