CONCERTED BREAKING OF TWO HYDROGEN BONDS IN WATER

CONCERTED BREAKING OF TWO HYDROGEN BONDS IN WATER HEXAMER PRISM REVEALED FROM BROADBAND ROTATIONAL SPECTROSCOPY JEREMY O RICHARDSON, CRISTOBAL PEREZ, SIMON LOBSIGER, ADAM A. REID, BERHANE TEMELSO, GEORGE C. SHIELDS, ZBIGNIEW KISIEL, DAVID J. WALES, BROOKS PATE, STUART C. ALTHORPE

2 Tunneling Motions in Water Clusters: Water Dimer Max Planck Institute for the Structure and Dynamics of Matter

3 Tunneling Motions in Water Clusters: Water Trimer Flip Bifurcations Max Planck Institute for the Structure and Dynamics of Matter

4 Tunneling Motions in Water Clusters: Water Hexamer Flip Tunneling Max Planck Institute for the Structure and Dynamics of Matter Bifurcation Tunneling

5 Tunneling Motions in Water Clusters: Water Octamer Tunneling splitting below experimental resolution Max Planck Institute for the Structure and Dynamics of Matter Science 352, 1194 (2016)

6 CP-FTMW Spectrometer (2 -18 GHz) at UVa 1) Improved signal averaging throughput (Tektronix) makes it possible to signal average to 10 M FIDs 2) Low-noise TWTA (400 W) 3) High directionality microwave horn antennas 4) Multinozzle (5) capability Time reduction: (5)2 = 25 Sample reduction: 5 Macroscopic Dipole Max Planck Institute for the Structure and Dynamics of Matter

7 Rotational Spectrum: Isomers of the Water Hexamer Prism Cage Only the Hexamer Prism shows tunneling Max Planck Institute for the Structure and Dynamics of Matter Book

8 Hydrogen Bond Networks in Water Hexamer Prism Structures: RI-MP 2/aug-cc-p. VDZ Energies: RI-MP 2/CBS Rotational Constants A B C 1698 MHz 1416 MHz 1358 MHz Experiment 1699 MHz 1366 MHz 1334 MHz Max Planck Institute for the Structure and Dynamics of Matter 1708 MHz 1430 MHz 1270 MHz 1658. 22 MHz 1362. 00 MHz 1313. 12 MHz

9 Hydrogen Bond Networks in Water Hexamer Prism 1) All 18 O/16 O permutations (Double and triple) 2) The HOD(H 2 O)5 isomers 3) All three water hexamers (64 + 12) x 3 = 228 spectra 76 Spectra for the Hexamer Water Prism! Max Planck Institute for the Structure and Dynamics of Matter

10 Hydrogen Bond Networks in Water Hexamer Prism 18 O 16 O Max Planck Institute for the Structure and Dynamics of Matter

11 Tunneling Patterns in the Hexamer Prism Rotational Spectrum Max Planck Institute for the Structure and Dynamics of Matter

12 Hexamer Prism Instanton Concerted Tunneling Pathways anti-geared Science 351, 1310 (2016) Max Planck Institute for the Structure and Dynamics of Matter

13 Hexamer Prism Instanton Concerted Tunneling Pathways 8 Equivalent minima geared antigeared Ground state energy levels HBB 2 -pol and MB-pol potentials give similar tunneling rates Max Planck Institute for the Structure and Dynamics of Matter

14 Summary • Isotopic substitution can be used to establish the water cluster structure and to shed light on the monomers involved in the tunneling dynamics. • The geared motion involves the concerted breaking of two hydrogen bonds. • The donor-acceptor tunneling has two concerted pathways that have comparable tunneling rates. • Tunneling is observed such that the motion of the oxygen atoms is minimized. • Current water potentials show good accuracy for tunneling rates. Max Planck Institute for the Structure and Dynamics of Matter

15 Acknowledgement Thank you for your attention! Max Planck Institute for the Structure and Dynamics of Matter