Presentation on theme: "IDENTIFICATION OF THE CAGE, PRISM, AND BOOK ISOMERS OF WATER HEXAMER AND THE PREDICTED LOWEST ENERGY HEPTAMER AND NONAMER CLUSTERS BY BROADBAND ROTATIONAL."— Presentation transcript:
IDENTIFICATION OF THE CAGE, PRISM, AND BOOK ISOMERS OF WATER HEXAMER AND THE PREDICTED LOWEST ENERGY HEPTAMER AND NONAMER CLUSTERS BY BROADBAND ROTATIONAL SPECTROSCOPY CRISTÓBAL PÉREZ, MATT T. MUCKLE, DANIEL P.ZALESKI, NATHAN SEIFERT, BROOKS H. PATE. Department of Chemistry. University of Virginia. ZBIGNIEW KISIEL. Institute of Physics, Polish Academy of Sciences. Poland. BERHANE TEMELSO, GEORGE C. SHIELDS, Dean’s Office, College of Arts and Sciences, and Department of Chemistry, Bucknell University.
Previous Studies DimerTrimer Tetramer Pentamer Liu, K.; Brown, et al. Nature 1996, 381, 501. Liu, K.; Brown, M.G.; Cruzan, J.D.; Saykally, R.J. Science 1996, 271, 62. Pugliano, N.; Saykally, R.J. Science 1996, 257, Cruzan, J.D. et al Science 1996, 271, 59. Hexamer “Cage” Saykally’s group Extensive work in water clusters by THz VRT Spectroscopy observing trimer, tetramer, pentamer and “cage” form of the water hexamer. Figures from R. J. Saykally and D. J. Wales, Science 336, 814 (2012)
Water Hexamer Extensively studied ab-initio as a benchmark system. Structural transition point wherein three-dimensional structures become more stable than the planar ring structures for the smaller clusters. Several low-energy isomers predicted: Prism, Cage and Book within an energy separation of 1 kJ/mol or less. Figures from: Bates, D.M.; Tschumper, G.S. J. Phys. Chem. A 2009, 113, 3555
Water Hexamer Cyclic, planar, S 6 hexamer has been found using HENDI Spectroscopy K. Nauta, R. E. Miller, Science, 287, 293 (2000). Hexamer Cage has been found using terahertz VRT Spectroscopy Liu, K. et al. Nature, 381, 501 (1996). Hexamer book found using IR spectroscopy coupled with size-selection techniques in OH stretch region. Steinbach, C. et al. PCCP, 6, 3320 (2004). E. G. Diken, et al., J. Phys. Chem. A 108, 64 (2004). No direct Structural Information
CP-FTMW Experiment CP-FTMW Spectroscopy in the 7-18 GHz frequency range. Optimal results found using a gas mixture of neon blown over a reservoir of DI water at a total pressure of 6 RT. 18 O isotopomer measurements with a reservoir mixture of 1:6 H 2 18 O/H 2 16 O using Ne as carrier gas at a total pressure of 6 RT. Brown, G. G.; Dian, B.C.; Douglass, K. O.; Geyer, S. M.; Shipman, S. T.; Pate, B. H. Rev. Sci. Instru. 2008, 79,
Results The water dimer shows the most intense spectrum.. Hexamer Cage shows a 200:1 signal-to noise ratio. Hexamer prism is the only one to show tunneling. Heptamer “prism” and Nonamer also assigned on basis of rotational constants. Trimer, tetramer and pentamer are nonpolar in their ground state. 650,000 averages spectrum and simulations for the assigned species Science 336, (2012).
Results ExperimentalTheory EquilibriumVib. Averaged Hexamer Cage A /MHz B /MHz C /MHz (8) (5) (5) Hexamer Prism A /MHz B /MHz C /MHz (4) (2) (2) Hexamer Book A /MHz B /MHz C /MHz (8) (6) (3) Vibrationally averaged structures provided by Shields group. Science 336, (2012).
Results ExperimentalTheory EquilibriumVib. Avg. Heptamer PR1 A /MHz B /MHz C /MHz (3) (6) (6) Nonamer D2dDD A /MHz B /MHz C /MHz (7) (6) (5) Science 336, (2012).
In Neon estimated population ratio for cage:prism:book is 4:4:1. In Argon only the cage is observed, giving evidence that the cage global-minimum energy structure for the water hexamer. Heptamer and Nonamer are observed in argon global-minimum configurations. Population and Isotopic Substitution Assignment of 6 separate rotational spectra, each one with a single 18 O water incorporated in the structure of the cluster. Science 336, (2012). † - prism transitions ‡ - book transitions ^ - heptamer transitions Ruoff, R.S et al. J. Chem. Phys. 1990, 93, 3142.
Population and Isotopic Substitution Science 336, (2012). None of them showing fine structure Tunneling quenched upon isotopic substitution
Population and Isotopic Substitution Science 336, (2012).
Population and Isotopic Substitution (A,B,C) = (I A,I B,I C ) I = Σ m i ∙r i 2 (A ˊ,B ˊ,C ˊ ) = (I A ˊ,I B ˊ,I C ˊ ) |r a |,|r b |,|r c | H 2 18 O
Hexamer Substitution Structures Equilibrium Structures B. Temelso, et al. B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011). Vibrationally averaged structures provided by Shields group NEXT TALK R 0 Structure.
Heptamer Substitution Structure To get all 18 O transitions resolvable at signal-to-noise ratio > 3:1. Reduced bandwidth Spectra (250MHz-1GHz) Much deeper average was required. New oscilloscope made this possible, recording 2 million FIDs overnight (NS Spectrum FIDs in two days with the old Scope). Repetition rate is limited by pumping speed. 100Gs/s 33GHz 12x Faster.
Heptamer Substitution Structure Seven separate broadband spectra upon isotopic substitution! MHz Bandwidth (7500MHz-7750MHz) and 1.4million averages.
Heptamer Substitution Structure MP2/6311G++(d,p) vs r s structure B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011). NEXT TALK! Structural analysis to obtain two experimental structures. Ro structure Rm1 structure RH03
Acknowledgements National Science Foundation (NSF) grants CHE and CHE The Institute of Physics, Polish Academy of Sciences (Poland). National Science Foundation (NSF) grants CHE , CHE , and CHE as part of the MERCURY high-performance computer consortium (www.mercuryconsortium.org). Thanks for your attention!