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:
1IDENTIFICATION OF THE CAGE, PRISM, AND BOOK ISOMERS OF WATER HEXAMER AND THE PREDICTED LOWEST ENERGY HEPTAMER AND NONAMER CLUSTERS BY BROADBAND ROTATIONAL SPECTROSCOPYCRISTÓBAL 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.
2Previous Studies Dimer Trimer Tetramer Pentamer Saykally’s group Extensive work in water clusters by THz VRT Spectroscopyobserving trimer, tetramer, pentamer and “cage” form of thewater hexamer.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, 257,1 937.Cruzan, J.D. et al Science 1996, 271, 59.Hexamer “Cage”Figures from R. J. Saykally and D. J. Wales, Science 336, 814 (2012)
3Water 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
4Water Hexamer Hexamer Cage has been found using terahertz VRT SpectroscopyLiu, K. et al. Nature, 381, 501 (1996).Hexamer book found using IR spectroscopy coupledwith 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).Cyclic, planar, S6 hexamer has been foundusing HENDI SpectroscopyK. Nauta, R. E. Miller, Science, 287, 293 (2000).No direct Structural Information
5CP-FTMW ExperimentCP-FTMW Spectroscopy in the 7-18 GHz frequency range.Optimal results found using a gas mixtureof neon blown over a reservoir of DI waterat a total pressure of 6 RT.18O isotopomer measurements with a reservoirmixture of 1:6 H218O/H216O using Ne as carriergas 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,
6Results650,000 averages spectrum and simulations for the assigned speciesThe 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.Science 336, (2012).
7Results Experimental Theory Hexamer Cage Hexamer Prism Hexamer Book ExperimentalTheoryEquilibriumVib. AveragedHexamer CageA /MHzB /MHzC /MHz(8)(5)(5)2249.21149.81097.9Hexamer Prism(4)(2)(2)1697.21416.61358.3Hexamer Book(8)(6)(3)1898.31106.3809.5Vibrationally averaged structures provided by Shields group.Science 336, (2012).
8Results Experimental Theory Equilibrium Vib. Avg. Heptamer PR1 A /MHz ExperimentalTheoryEquilibriumVib. Avg.Heptamer PR1A /MHzB /MHzC /MHz(3)(6)(6)1333.7974.1954.21297.5950.7926.8Nonamer D2dDD(7)(6)(5)810.9630.6585.9791.2619.8574.1Science 336, (2012).
9Population and Isotopic Substitution 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.† - prism transitions‡ - book transitions^ - heptamer transitionsAssignment of 6 separaterotational spectra, each onewith a single 18O waterincorporated in the structureof the cluster.Ruoff, R.S et al. J. Chem. Phys. 1990, 93, 3142.Science 336, (2012).
10Population and Isotopic Substitution None of them showingfine structureTunneling quenched uponisotopic substitutionScience 336, (2012).
11Population and Isotopic Substitution Science 336, (2012).
12I = Σ mi∙ri2 |ra|,|rb|,|rc| (A,B,C) = (IA,IB,IC) Population and Isotopic SubstitutionH218O(A,B,C) = (IA,IB,IC)(Aˊ,Bˊ,Cˊ) = (IAˊ,IBˊ,ICˊ)I = Σ mi∙ri2|ra|,|rb|,|rc|
13Hexamer Substitution Structures Equilibrium StructuresB. Temelso, et al.Vibrationally averagedstructures providedby Shields groupNEXT TALKR0 Structure.B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011).
14Heptamer Substitution Structure To get all 18O 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 33GHz12x Faster.
15Heptamer Substitution Structure 250MHz Bandwidth (7500MHz-7750MHz) and 1.4million averages.Seven separate broadband spectra upon isotopic substitution!
16Heptamer Substitution Structure MP2/6311G++(d,p) vs rs structureNEXT TALK!Structural analysis to obtaintwo experimental structures.Ro structureRm1 structureRH03B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011).
18Thanks for your attention! AcknowledgementsNational Science Foundation (NSF) grants CHE and CHEThe Institute of Physics, Polish Academy of Sciences (Poland).National Science Foundation (NSF) grants CHE , CHE ,and CHE as part of the MERCURY high-performance computerconsortium (www.mercuryconsortium.org).Thanks for your attention!