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 (
Thanks for your attention!