1. Protonated Water Clusters Revisited: Investigating the Elusive Excess Proton Vibrational Signature using Cryogenic Ion Spectroscopy Joseph Fournier, Christopher Johnson, Conrad Wolke, Arron Wolk, Gary Weddle, and Mark Johnson 69 th International Symposium on Molecular Spectroscopy June 19, 2014

2. “Eigen”“Zundel”“Eigen” H9O4+H9O4+ H5O2+H5O2+ H9O4+H9O4+ Mobility of the Excess Proton in Water

3. Vibrational Signatures of the Eigen and Zundel Motifs: Johnson, Duncan, Jordan, Science, 308, 1764 (2005)

4. Mass Spectrum of H + (H 2 O) n : The “Magic” H + (H 2 O) 21 Cluster 708090100110120130140 Ion Intensity (arb. unit) Time (μs) * n=21

5. Vibrational Spectra of Larger Clusters and the “Magic” n=21 MAJ, MAD, KDJ, Science, 304, 1137 (2004) AD AAD

6. 20002200240026002800300032003400360038004000 Photon Energy (cm -1 ) H3O+H3O+ F S A Spectroscopic Evidence of the Dodecahedral H + (H 2 O) 21 Structure: Where are the Predicted Surface-Bound Eigen Bands? NO Bands in Sight!!!

7. Photon Energy (cm -1 ) Vibrational Spectra Near the Magic n=21 Cluster: Water Loss vs H 2 Predissociation from Clusters formed in a Supersonic Jet Still No Proton Bands! A. Fujii, J. Phys. Chem. Lett. 2, 2130 (2011) Need to Search the Spectroscopic Badlands! and have COLDER ions AD

8. Flash Forward 10 Years: Can We Recover the Excess Proton Bands using Cryogenically Processed Ions? ESI Needle Temperature Controlled Ion Trap Mounted to He Cryostat Ion Optics 2m Flight Tube Wiley- McLaren TOF Reflectron-1 Coaxial TOF Reflectron-2 e-e- DC-Turning Quad Pulsed Valve Electron Gun Photoelectron Imager MCP Detector MCP Detector Nd:YAG OPO/OPA Tunable IR 600-4500 cm -1 Nd:YAG OPO/OPA Tunable IR 600-4500 cm -1 Nd:YAG Ion Optics Differential Aperture Skimmers Heated Capillary RF-Ion Guides Instrument Control Wavemeter

9. ESI Needle RF-Ion Guides 72747678 Time of Flight (  s) 30 ms 50 ms 40 ms 20 ms 10 ms doubly-charged parent a) b) c) d) e) trap residence time: Signal Intensity (arbitrary units) hydrogen adduct formation 5 10 15 * Cryogenic Ion Trap Temperature Controlled Helium Cryostat 4 to 300 K 10% H 2 or D 2 in He Buffer Gas + + + + Cooled close to vibrational zero point Condense lightly bound “tags” Cryogenic Ion Vibrational Predissociation Spectroscopy

10. 8001200160020002400280032003600 Photon Energy (cm -1 ) Librations H 2 O bends ν bound AAD ν DDA ν free AAD A B C D E F G H ν a H3O+H3O+ ν umb H3O+H3O+ ν s H3O+H3O+ ν a H3O+H3O+ ν s H3O+H3O+ D 2 -Tagging in a Cryogenically Cooled Ion Trap Torrent-Sucarrat and Anglada, JCTC, 7, 467 (2011) Harmonic H 2 O Loss H 2 tag, jet D 2 tag, ion trap Librations Bend

11. 8001200160020002400280032003600 Photon Energy (cm -1 ) A B C D E F G H ν a H3O+H3O+ ν s H3O+H3O+ D 2 -Tagging in a Cryogenically Cooled Ion Trap Harmonic H 2 O Loss H 2 tag, jet D 2 tag, ion trap Librations Bend Cs + (H 2 O) 20

12. 8001200160020002400280032003600 Photon Energy (cm -1 ) H 2 O bend Librations ν bound AAD ν free AAD ν DDA ν Association Band OH stretches ‡ DDA AAD νsνs νaνa 1.034 Å 1.020 Å 108 o 112 o n = 21 n = 4 1.035 Å 1.033 Å ν a H3O+H3O+ ν umb H3O+H3O+ Comparison of n=21 with Eigen and Bulk Water Water 1M HCl Science, 344, 1009 (2014) bend

13. H + (H 2 O) n n=2 3 4 5 6 10 14 18 21 Evolution of the Excess Proton Band with Cluster Size: Connecting 2005 to 2014 800120016002000240028003200 36004000 Photon Energy (cm -1 ) 400

14. Beyond H + (H 2 O) 21 8001200160020002400280032003600 Photon Energy (cm -1 ) D 2 Predissociation Yield H + (H 2 O) 24 H + (H 2 O) 28 H + (H 2 O) 21 Proton signature(s) remain constant, but are losing their structure H + (aq)

15. Prof. Mark Johnson Prof. Gary Weddle Prof. Chris Johnson Dr. Arron Wolk Dr. Andrew DeBlase Conrad Wolke Olga Gorlova Stephanie Craig Patrick Kelleher Acknowledgments Asmis Lab Nadja Heine Prof. Knut Asmis

16. 80012001600200024002800 Pred. Yield Photon Energy (cm -1 ) Calc. Anh. Int. H 3 O + asym. Librations + Eigen H 2 O bends VPT2 B3LYP/6-31+G(d) Calculations (with anharmonic intensities) Association Band? H 2 O bend H 3 O + umb.

17. Watching the Bands Shift in D + (D 2 O) 21 D + (D 2 O) 21 600100014001800220026003000 D 2 Predissocation Yield Photon Energy (cm -1 ) H + (H 2 O) 21 2600280030003200340036003800 A B C D E F G H A B C D E F G H ν free AAD ν free AAD A, B: third shell DDA asym. Plausible Assignments (cam-B3LYP/6-31+G(d)): C: coupled H 2 O (H 3 O + ) asym., DDA D: coupled H 2 O (H 3 O + ) sym., DDA E: DDA OH stretches F - H: AAD bound OH stretches H 2 O bend overtone

18. 4008001200160020002400280032003600 Photon Energy / cm -1 338 cm -1 530 cm -1 625 and 674 cm -1

19. Evolution of the Excess Proton Band with Cluster Size H + (H 2 O) 4 8001200160020002400280032003600 Photon Energy (cm -1 ) H + (H 2 O) 10 H + (H 2 O) 14 H + (H 2 O) 18 H + (H 2 O) 21 AD AAD ? DDA All Eigen H 2 O DDA Increased Eigen distortion and/or solvation effect Formation of clathrate-like cage x3

20. D 2 Pred. Yield 8001200160020002400280032003600 Ar Pred. Yield Photon Energy (cm -1 )

21. 8001200160020002400280032003600 Photon Energy (cm -1 ) α ~ H 3 O + umbrella H 3 O + rocks ν H 3 O + umb.+ rocks rock+ rock ν H 3 O + harmonic ν Zundel ~ harmonic

22. D 2 Pred. Yield 2400260028003000320036003800 Ion Dip Signal Photon Energy (cm -1 ) Two-Color Enhancement Bare H + (H 2 O) 4

23. Two-Color Enhancement 24002600280030003200340036003800 D 2 /H 2 O yield Photon Energy (cm -1 ) D 2 tag Probe