title: Structure and torsional dynamics of the water octamer from THz laser spectroscopy near 215 μm.
abstract: Clusters of eight water molecules play an important role in theoretical analysis of aqueous structure and dynamics but have proven to be challenging experimental targets. Here we report the high-resolution spectroscopic characterization of the water octamer. Terahertz (THz) vibration-rotation-tunneling (VRT) spectroscopy resolved 99 transitions with 1 part per million precision in a narrow range near 46.5 wave numbers, which were assigned to the h16 octamer via detailed isotope dilution experiments. Fitting to a semi-rigid symmetric top model supports predictions of two coexisting cuboidal structures and provides precise values for the changes in their rotational constants. Comparison with theory and previous spectroscopic data provides a characterization of the two structures and the observed torsional vibration and supports the prediction that the D2d symmetry structure is lower in energy than the S4 isomer.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94705, USA.
authors.forename: William T S
authors.initials: WT
authors.lastname: Cole
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK.
authors.forename: James D
authors.initials: JD
authors.lastname: Farrell
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK. saykally@berkeley.edu dw34@cam.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Wales
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94705, USA. saykally@berkeley.edu dw34@cam.ac.uk.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Saykally