Isomer-specific Spectroscopy of Benzene-(water)n Clusters with n=2-6: 69th International Symposium on Molecular Spectroscopy 11/15/2018 Isomer-specific Spectroscopy of Benzene-(water)n Clusters with n=2-6: The effects of benzene on water cluster structure Graduate students: Evan Buchanan (NIST) Jacob Dean (Toronto) Nathan Kidwell (Penn) Deepali Mehta-Hurt Joseph Korn Di Zhang Joe Gord Nicole Burke Patrick Walsh Daniel Hewett John Hopkins Post-doc: Dr. Ryoji Kusaka (RIKEN) Undergraduates: Polina Novotnaya (Univ. Chicago) Rachel Clayton (P&G) Alex Parobek (Yale) Collaborators: Christian Müller (Bochum) Sam Gellman (UW-Madison) Scott McLuckey (Purdue) Ned Sibert (UW-Madison) David Plusquellic (NIST) Lyudmila Slipchenko (Purdue) Brooks Pate (UVa) Hyuk Kang (Ajou, Korea) Funding 11/15/2018 1 1

Benzene-(H2O)n Reprise Bz-(H2O)1 Bz-(H2O)2 Bz-(H2O)3 Bz-(H2O)4 1:5 1:6 1:7 R.N. Pribble and T.S. Zwier, "Size-Specific Infrared Spectra of Benzene-(H2O)n with n=1-7: Evidence for the Transition from Cyclic to Non-cyclic (H2O)n structures", Science 265, 75-79 (1994). Motivations Better IR sources Extension to bending mode region Under-analyzed spectra – better theory How does benzene perturb the water clusters? Comparison with other aromatic solutes

Detection Schemes: R2PI Resonant two-photon ionization Time-of- Flight Mass spec S0 S1 Bz*-(H2O)n Bz-(H2O)1 Bz-(H2O)2 Bz-(H2O)3 Bz-(H2O)4 Bz-(H2O)5 Bz-(H2O)6 Bz-(H2O7) 1:1+ 1:2+ 1:3+ 1:4+ 1:5+ 258.5 258.0 257.5 UV Wavelength (nm) Bz+-(H2O)n+e- Bz-(H2O)n

Resonant Ion-Dip Infrared Spectroscopy Records the IR spectrum of a single conformation free from interference from others present in the expansion Dt=100 nsec Cold initial population distribution IR Hole-burn laser Probe laser R2PI S0 S1 A++e- A*(S1) I(no HB) a Popnbefore I(signal)= I(HB) – I(no HB) I(no HB) a Popnafter

Overview RIDIR spectra of benzene-(H2O)n in the OH stretch region Ryoji Kusaka Π Σ Bz-(H2O)1 1:5 1:6 1:7 Bz-(H2O)2 Bz-(H2O)3 Bz-(H2O)4 Water Cycles Free, pi, H-bonded. Wavenumber range spanned by OH stretch spectra. Talk about n=2-6 Low IR power 3D structures High IR power

RIDIR spectra of Bz-(H2O)n in the OH bend region Bz-(H2O)2 Bz-(H2O)3 Bz-(H2O)4 Bz-(H2O) 1:5 1:6 1:7 1:8 (S4) 1:8(D2d) 1600 1650 1700 1750 Wavenumbers (cm-1) p Water Cycles 3D structures Cubes Y Much smaller freq shifts 1 bend per H2O Frequency of OH bend increases as strength of H-bonds increases

Experimental RIDIR Spectra compared to calc’n Benzene-(H2O)2 Experimental RIDIR Spectra compared to calc’n p SS/AS OH Stretch D p/SS p/AS F D F p 1595 cm-1 H2O monomer D OH Bend p D M06-2x/6-311++g(2d,p) 7

Experimental RIDIR Spectra compared to calc’n Benzene-(H2O)3 Experimental RIDIR Spectra compared to calc’n 3 OH Stretch Strong 2 Weak 1 2 3 1 OH Bend Weak Strong 2 1 3 M062x/6-311++g(2d,p) 8

Benzene-(H2O)3 : Perturbing the Trimer Cycle +- 1.91 Å -+ All AD (H2O)3 1.89 Å 1.89 Å +++ Shorten 3 1.86 Å 2 1 1.88 Å Bz-(H2O)3 1 Now ADd 3 2.01 Å 1(p) 2 Lengthen 2 3 M06-2X/6-311++g(2d,p) 9

Experimental RIDIR Spectra compared to Calcn Benzene-(H2O)4: Experimental RIDIR Spectra compared to Calcn 4 Bend Overtone? 3 OH Stretch 2 1 4 3 1 Free 2/3/4 2 Mixing 1p TSZ Added the intensities of the 1658.8+1657.6 (95+50=145) and put in single line. 3 OH Bend 1/2 4 M06-2X/6-311++g(2d,p) 10

Benzene-(H2O)4 : Perturbing the Tetramer Cycle 1.77 Å 2 nodes -o+o o+o- 1.77 Å (H2O)4 1.77 Å 1.77 Å 0 nodes ++++ 3 4 nodes -+-+ 1.75 Å 1.81 Å Bz-(H2O)4 4 2 2 4 3 1 Shorten 1.75 Å Mixing Free 2/3/4 1.84 Å 1p 1 Lengthen M062x/6-311++g(2d,p) 11

Experimental RIDIR Spectra compared to Calcn Benzene-(H2O)5: Experimental RIDIR Spectra compared to Calcn 1 2 3 4 5 4 F p 5 H-bonded OH…O Bend Overtone M062x/6-311++g(2d,p) 12

Benzene-(H2O)5 : Perturbing the Pentamer cycle +++-- 1.76 Å -o++- 1.74 Å 2 nodes 1.74 Å 1.73 Å 1.73 Å 4 nodes 1.71 Å 1.72 Å 1.75 Å 1.78 Å 1.80 Å Lengthen 2 0 nodes -o+-+ +++++ -+-++ 1 oo++- o--+o 3 ooo++ ++-oo Shorten +-ooo p 4 5 M062x/6-311++g(2d,p) 13

Experimental RIDIR Spectra compared to Calcn Benzene-(H2O)6: Experimental RIDIR Spectra compared to Calcn AAD AD ApD ADD p Free 4 Free OH Stretches X5 4 Free OH grps Water hexamer: Cage Prism Book Benzene is a book binder! M06-2X/6-311++g(2d,p) 14

Benzene-(H2O)6 : Perturbation to Hexamer Book 3 1.71Å Mixed 1/2/6 (H2O)6 1.71 Å 1.84 Å 1.98Å 1 Mixed 3/4/5 1.69 Å 4 1.82 Å ADD(3 across) 6 Smaller tetramer 1.81 Å 5 Larger tetramer F(5) Lengthen 1.73 Å 1.79 Å 1.93Å Bz-(H2O)6 1.87 Å 1.64 Å AD(2) AD(5) AD(4) AAD(6) AdD(1) ADD(3) ADD(3) Free(2,4,5,6) Shorten 1.78 Å p(1) 1.80 Å M06-2X/6-311++g(2d,p) 15

OH stretch region of BW6 Bend overtones Free(2,4,5,6) AD(2) ADD(3) AAD(6) AD(2) AdD(1) AD(5) AD(4) ADD(3) p(1) Free(2,4,5,6) Bend overtones 1 2 3 4 5 6 ADD AdD AAD

Scaling Factors y = 0.8014.x + 550 17

Scaling Factor Comparison: Benzene-(H2O)6 18

Benzene-(H2O)5,6 Bending Region ooo++ oo++- -+-+o +-+oo ADD(3) Mixed 5/6 1/2 AD(4) 2 1 3 5 4 Exptl artifact or deficiency of calc’ns or mode-specific effects? M062x/6-311++g(2d,p) 19

Other aromatic solutes Tricyclophane-(H2O)n n=1-5 DPOE-(H2O)n n=1-4 Benzene-(H2O)n n=1-8 E.G. Buchanan, J.R. Gord, and T.S. Zwier, “Solvent Effects on Vibronic Coupling in a Flexible Bichromophore: Electronic Localization and Energy Transfer induced by a Single Water Molecule”, J. Phys. Chem. Lett. 4, 1644-1648 (2013). P.S. Walsh, E.G. Buchanan, J.R. Gord and T.S. Zwier, “Solvent-mediated Internal Conversion in Diphenoxyethane-(H2O)n clusters”, n=2-4”, (in preparation). Evan G. Buchanan and Timothy S. Zwier, “Binding Water Clusters to an Aromatic-rich Hydrophobic Pocket: [2.2.2]Paracyclophane-(H2O)n, n=1-5”, J. Phys. Chem. A. (ASAP). DOI: 10.1021/jp502998b

The Zwier Group Acknowledgements Ned Sibert David Plusquellic Scott Sam Gellman Scott McLuckey

Scaling Factor Comparison: Benzene-(H2O)4 22

Scaling Factor Comparison: Benzene-(H2O)5 23