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IDENTIFICATION OF THE CAGE, PRISM, AND BOOK ISOMERS OF WATER HEXAMER AND THE PREDICTED LOWEST ENERGY HEPTAMER AND NONAMER CLUSTERS BY BROADBAND ROTATIONAL.

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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:

1 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.

2 Previous Studies Dimer Trimer Tetramer Pentamer Saykally’s group
Extensive work in water clusters by THz VRT Spectroscopy observing trimer, tetramer, pentamer and “cage” form of the water 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)

3 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

4 Water Hexamer 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). Cyclic, planar, S6 hexamer has been found using HENDI Spectroscopy K. Nauta, R. E. Miller, Science, 287, 293 (2000). No direct Structural Information

5 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. 18O isotopomer measurements with a reservoir mixture of 1:6 H218O/H216O 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,

6 Results 650,000 averages spectrum and simulations for the assigned species 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. Science 336, (2012).

7 Results Experimental Theory Hexamer Cage Hexamer Prism Hexamer Book
Experimental Theory Equilibrium Vib. Averaged Hexamer Cage A /MHz B /MHz C /MHz (8) (5) (5) 2249.2 1149.8 1097.9 Hexamer Prism (4) (2) (2) 1697.2 1416.6 1358.3 Hexamer Book (8) (6) (3) 1898.3 1106.3 809.5 Vibrationally averaged structures provided by Shields group. Science 336, (2012).

8 Results Experimental Theory Equilibrium Vib. Avg. Heptamer PR1 A /MHz
Experimental Theory Equilibrium Vib. Avg. Heptamer PR1 A /MHz B /MHz C /MHz (3) (6) (6) 1333.7 974.1 954.2 1297.5 950.7 926.8 Nonamer D2dDD (7) (6) (5) 810.9 630.6 585.9 791.2 619.8 574.1 Science 336, (2012).

9 Population 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 transitions Assignment of 6 separate rotational spectra, each one with a single 18O water incorporated in the structure of the cluster. Ruoff, R.S et al. J. Chem. Phys. 1990, 93, 3142. Science 336, (2012).

10 Population and Isotopic Substitution
None of them showing fine structure Tunneling quenched upon isotopic substitution Science 336, (2012).

11 Population and Isotopic Substitution
Science 336, (2012).

12 I = Σ mi∙ri2 |ra|,|rb|,|rc| (A,B,C) = (IA,IB,IC)
Population and Isotopic Substitution H218O (A,B,C) = (IA,IB,IC) (Aˊ,Bˊ,Cˊ) = (IAˊ,IBˊ,ICˊ) I = Σ mi∙ri2 |ra|,|rb|,|rc|

13 Hexamer Substitution Structures
Equilibrium Structures B. Temelso, et al. Vibrationally averaged structures provided by Shields group NEXT TALK R0 Structure. B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011).

14 Heptamer 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 33GHz 12x Faster.

15 Heptamer Substitution Structure
250MHz Bandwidth (7500MHz-7750MHz) and 1.4million averages. Seven separate broadband spectra upon isotopic substitution!

16 Heptamer Substitution Structure
MP2/6311G++(d,p) vs rs structure NEXT TALK! Structural analysis to obtain two experimental structures. Ro structure Rm1 structure RH03 B. Temelso, K. A. Archer, G. C. Shields, J. Phys. Chem. A, 115, (2011).

17 Residual Spectrum

18 Thanks for your attention!
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!


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