Three-Dimensional Water Networks Solvating an Excess Positive Charge: New Insights into the Molecular Physics of Ion Hydration Conrad T. Wolke Johnson Group June 24, 2015 International Symposium on Molecular Spectroscopy

Microhydration of Cs + (H 2 O) 20  Cs + (H 2 O) 20 is a “Magic” cluster  Predict structure from MS (Castleman, 1991)  Identify structure by the band pattern of free OH stretch (Williams, 2013) Cooper et al., JPCA, 117, 6571 (2013) Selinger et al., JPC, 95, 8442 (1991) Photon Energy (cm -1 ) Bound OH stretches B3LYP/ 6-31+G** Pentagonal Dodecahedron AAD AD Free OH stretch

ESI Temperature Controlled Ion Trap Ion Optics Flight Tube Wiley- McLaren TOF Reflectron Turning Quad MCP Nd:YAG OPO/OPA Tunable IR cm -1 RF-Ion Guides Wavemeter 2-4 kV Dry Air mM Solution 1 st Skimmer Capillary ESI Needle H 2 O/D 2 O P Pressure 1 st Diff. Stage Tandem Time of Flight Mass Spectrometer

Infrared Spectrum of Cs + (H 2 O) 20 Norm. Int. (a.u.) Mass to Charge Ratio (amu/e) Cs + (H 2 O) 20  Using D 2 messenger tagging to acquire complete IR predissociation spectrum of cold Cs + hydrates from 400 to 3800 cm -1 Cooper et al., JPCA, 117, 6571 (2013) Fournier et al., PNAS, 111, (2014) OH stretches H 2 O bend Librations Calc. Int Photon Energy (cm -1 ) Pred. Yield (a.u.) Knut Asmis (Free Electron Laser) B3LYP/ G**

D 2 Predissociation Yield (a.u.) Photon Energy (cm -1 ) Effects of Deuteration: Cs + (D 2 O) 20  IR Bands of the H-bonded network still featureless  Deuteration causes the expected global red-shift of the IR spectrum Continuum resolves into distinct bands Cs + (H 2 O) 20 Cs + (D 2 O) 20

Refine Harmonic Calculations: Cs + (D 2 O) 20 D 2 Pred. Yield / Calc. Intensity (a.u.) Cs + (D 2 O) Photon Energy (cm -1 ) B3LYP/6-31++G** Schulz et al., CPC, 18, 98 (2002)  IR Bands of the H-bonded network still featureless  Deuteration causes the expected global red-shift of the IR spectrum Continuum resolves into distinct bands Use all IR features to match experiment with calculation

D 2 Pred. Yield / Calc. Intensity (a.u.) Cs + (D 2 O) Photon Energy (cm -1 ) B3LYP/6-31++G** Free AAD ADD 1 ADD 2 ADD 3 Refine Harmonic Calculations: Cs + (D 2 O) 20  One free OH stretch from AAD type water H-Bond acceptor (A) and donor (D)  Asymmetric bound OH stretches of ADD type waters  Corresponding bound AAD OH stretch and symmetric ADD stretches Schulz et al., CPC, 18, 98 (2002) Bound AAD sym asym

D 2 Pred. Yield / Calc. Intensity (a.u.) Cs + (D 2 O) Photon Energy (cm -1 ) B3LYP/6-31++G** Can we assign H-bonded OH stretches to individual types of water molecules? Refine Harmonic Calculations: Cs + (D 2 O) 20 Schulz et al., CPC, 18, 98 (2002) Free AAD Bound AAD ADD 1 ADD 2 ADD 3 sym asym

Photon Energy (cm -1 ) Cs + (H 2 O) 6 – Models for Solvation Mechanism Sotiris S. Xantheas PNNL James Lisy UIUC  Unbiased reproduction of IR spectra No Scaling  Exact mapping of the PES Ion – Water Water – Water D 2 Pred. Yield / Calc. Intensity (a.u.) Kolaski et al., JCP, 126, (2007) CCSD(T)/aug-cc-pVDZ MP2/aug-cc-pVTZ (VPT2) Cs + (H 2 O) 6

Assignment of Local Mode Patterns D 2 Pred. Yield / Calc. Int. (a.u.) Photon Energy (cm -1 ) CCSD(T)/aug-cc-pVDZ MP2/aug-cc-pVTZ (VPT2) Single Donor Cyclic Core Can we isolate a single H 2 O to prove the band assignment?

Spectral Isolation of Local Band Displacement Garand et al., Science, 335, 694 (2012) Stearns et al., PCCP, 11, 125 (2009) Large shifts from isotopic labeling of localized 15 N and 13 C atoms confine single transitions Minor contributions to the normal modes are also evident  How about non-covalent bonds?  Isolation of local band displacement contribution through isotopic labeling Etienne Garand C=O Stretch N-H Bend

ESI Temperature Controlled Ion Trap Ion Optics Flight Tube Reflectron MCP Nd:YAG OPO/OPA Tunable IR cm -1 Wavemeter Isotopic Labeling Scheme for H-Bonded Networks Wiley- McLaren TOF Turning Quad RF-Ion Guides 2-4 kV Dry Air mM Solution 1 st Skimmer Capillary ESI Needle D2OD2O P Pressure 1 st Diff. Stage Cs + (D 2 O) n + H 2 O vap Cs + (D 2 O) n-m (H 2 O) m

Relative Intensity (a.u.) Mass to Charge (amu/e) H 2 O exchange 5 67 Cs + (D 2 O) n MS Evidence: Does H 2 O stay intact? Liquid phase: 25% H 2 O H 2 O : D 2 O →50% HDO 25% D 2 O  Mass Spec spaced by 2 amu/Z  No HOD bending mode H 2 O stays intact Isotopic Labeling of Cs + (D 2 O) n-m (H 2 O) m D 2 Pred. Yield (a.u.) Photon Energy (cm -1 ) Cs + (D 2 O) 5 (H 2 O) HOH Bending IR Spectroscopic Evidence: HOD Bend D2OD2O H2OH2O

Cs + (D 2 O) 5 (H 2 O) Cs + (H 2 O) 6 Photon Energy (cm -1 )  Infrared spectrum of the isotopically labeled complex stays intact Each H 2 O adds its 2 individual modes All 6 position equally populated  FWHM of OH stretch bands are reduced Evidence for minor vibrational excitonic coupling Can we isolate modes from individual H 2 O molecules? 27cm -1 15cm -1 D 2 Predissociation Yield (a.u.) Spectral Manifestation of Cs + (D 2 O) 5 (H 2 O)

ESI Temperature Controlled Ion Trap Ion Optics Flight Tube Reflectron Coaxial TOF Reflectron MCP Nd:YAG OPO/OPA Tunable IR cm -1 Ion Optics RF-Ion Guides Wavemeter OPO/OPA Isotopomer Specific IR-IR Double Resonance Wiley- McLaren TOF Turning Quad Cs + (D 2 O) n + H 2 O vap Cs + (D 2 O) n-m (H 2 O) m

ESI Temperature Controlled Ion Trap Ion Optics Flight Tube Coaxial TOF Reflectron MCP Nd:YAG OPO/OPA Tunable IR cm -1 Ion Optics Wavemeter Isotopomer Specific IR-IR Double Resonance OPO/OPA Cs + (D 2 O) n + H 2 O vap Cs + (D 2 O) n-m (H 2 O) m RF-Ion Guides Wiley- McLaren TOF Turning Quad

Isotopomer Specific IR Spectra of Cs + (H 2 O)(D 2 O) N 2 Pred. Yield (a.u.) Photon Energy (cm -1 ) IR 2 MS 3 Signal Single Donor Cyclic Core

CIVP Spectrum IR 2 MS 3 Dip Signal T Trap = 10 K Photon Energy (cm -1 ) A B C D A B C D I – (H 2 O)(D 2 O) – Isotopomer Specific IR Spectra MP2/aug-cc-pVDZ(-PP)

CIVP Spectrum IR 2 MS 3 Dip Signal T Trap = 25 K Photon Energy (cm -1 ) A B C D A B C D I – (H 2 O)(D 2 O) – Isotopomer Specific IR Spectra MP2/aug-cc-pVDZ(-PP)

 Deuteration of large clathrate alkali hydrates resolves distinct patterns in the H-bonded water stretch continuum Conclusions Photon Energy (cm -1 ) Cs + (D 2 O) 20  Trace Isotope Scheme in the gas-phase allows labeling of an intact H 2 O  Spectral Isolation of the two OH stretching modes originating from a single H 2 O molecule  Vibrational Spectroscopy to unravel dynamical behavior in H-Bonded Networks Cs + (D 2 O) 5 (H 2 O)

Acknowledgments Johnson Group Joseph A. Fournier Olga Gorlova Stephanie M. Craig Joanna K. Denton Joseph W. DePalma Chinh H. Duong Patrick J. Kelleher Fabian S. Menges Gary H. Weddle Mark A. Johnson PNNL Evangelos Miliordos Sotiris S. Xantheas

Trap Temperature (K) Photon Energy (cm -1 ) Temperature Dependence of I ‒ (H 2 O) 2

Francesco Paesani, UCSD Molecular Dynamics of I ‒ (H 2 O) 2

Assignment of Local Mode Patterns D 2 Pred. Yield / Calc. Int. (a.u.) Photon Energy (cm -1 ) CCSD(T)/aug-cc-pVDZ MP2/aug-cc-pVTZ (anharmonic) Cyclic Core Single Donor IR 2 MS 3 Dip Signal

Conclusions 1.Precise Model for Ion solvation  Exact Predictions for Ion-Water and Water-Water interaction 2. Spectroscopic Isolation of a single isotopically labeled water molecule  Infrared Transitions  Chemical Environment Access to:  Dynamics  Phase Transitions of finite size systems

D 2 Predissociation Yield (a.u.) Photon Energy (cm -1 ) Cs + (H 2 O) 20 Cs + (D 2 O)

D 2 Predissociation Yield (a.u.) Photon Energy (cm -1 ) Cs + (H 2 O) 20 Cs + (D 2 O)

Microhydration of Monovalent Salts Cs + (H 2 O) n Cs + (H 2 O) 6 Photon Energy (cm -1 ) IR Absorption (a.u.)

Simulations of complex aqueous environments, require microscopic behavior of ions under restricted solvation Cluster spectra provide input for Ion-water intermolecular potential surface Paesani, F. et al., J. Chem. Theory Comput. 11, 1145 (2015) Xantheas, S.S. Et al., PCCP, 16, 6886 (2014) Motivation: Models for Ocean Surface Layer

 MD Calculation produced ̴1000 Structures  Refined by DFT yields the vibrational spectra  Minimum energy structure does not yield best Fit D 2 Pred. Yield / Calc. Intensity (a.u.) kcal/mol Cs + (D 2 O) 20 Photon Energy (cm -1 ) Schulz et al., PCCP, 5, 5021 (2003) Electronic Structure Calculations B3LYP/6-31++G**

N 2 Pred. Yield (a.u.) Photon Energy (cm -1 ) IR 2 MS 3 Dip Signal (a.u.) Isotopomer Specific IR Spectra of Cs + (H 2 O)(D 2 O) 5