1. Influence of Aromatic Molecules on the Structure and Spectroscopy of Water Clusters
Daniel Tabor1, Patrick Walsh2,
Timothy Zwier2, Edwin Sibert1
1University of Wisconsin—Madison
2Purdue University

2. Background (Water)n with n=3-5: cycles Bz-(H2O)n: H-bond with benzene
Developed model include effects of Fermi resonance
Lengthen
Going to add pictures, but these are the main points
Shorten

3. Summary of Bz-(H2O)n
Interaction with phenyl ring leads to ~55 cm-1 shift in free OH frequency
H-bond lengths in the cycle are systematically distorted
Exp
Theory
Intra + Fermi
3000
3200
3400
3600
3800
Wavenumber (cm-1)

4. DPOE and TCP
DPOE
TCP
Model system for studying the basic building blocks of polyethylene glycol
Prototypical macrocycle
Large aromatic binding pocket
Both a phenoxy oxygen and phenyl ring for water to interact with
J. Phys. Chem. A, 118, 8583–8596 (2014).
J. Chem. Phys. 142, (2015).

5. DPOE and TCP Where does the water go? DPOE TCP
Model system for studying the basic building blocks of polyethylene glycol
Prototypical macrocycle
Large aromatic binding pocket
Both a phenoxy oxygen and phenyl ring for water to interact with
J. Phys. Chem. A, 118, 8583–8596 (2014).
J. Chem. Phys. 142, (2015).

6. Resonant Two-Photon Ionization Resonant Ion-Dip Infrared Spectroscopy
Experimental Method
R2PI
Resonant Two-Photon Ionization
RIDIR
Resonant Ion-Dip Infrared Spectroscopy
M (S0)
M* (S1)
M++ e-
M (S0)
M* (S1)
M++ e-
Records the IR spectrum of a single conformation free from interference from others present in the expansion
I(signal)=
I(HB) – I(no HB)
20 Hz
20 Hz
These are of course, the real colors used in the experimental lasers 
Δt=200ns
10 Hz

7. Model Hamiltonian Construction
Normal Modes
Form Local Mode Basis
Scale
Add Anharmonicity
Spectra

8. Transformation from Normal to Local Modes
Normal Mode Scissors
Normal Mode OH Stretches
Normal Mode
Local Mode

9. Transformation from Normal to Local Modes
Normal Mode Scissors
Normal Mode OH Stretches
Unscaled Local Stretches
Unscaled Local Scissors
Normal Mode
Local Mode

10. Transformation from Normal to Local Modes
Normal Mode Scissors
Normal Mode OH Stretches
Unscaled Local Stretches
Unscaled Local Scissors
Normal Mode
Scaled Local Scissors
Scaled Local
Stretches
Local Mode

11. Hamiltonian Matrices DPOE-H2O DPOE-W1 Exp Full Model H2O
Wavenumber (cm-1)
The label D is for it being a weaker donor than a full D. Analogy to a vs. A in the benzene water work.
Even a little donor character shifts the intramonomer coupling down by 10 cm-1
2.64 Å
2.02 Å
“d” shift: 86 cm-1

12. Hamiltonian Matrices DPOE-(H2O)2 Exp Full Model Intra + Fermi
Wavenumber (cm-1)
The pure H2O dimer H-Bond distance is 1.93 at this level of theory, so the donor pulls in the H bond as expected
1.87 Å
1.96 Å
2.64 Å
“d” shift: 120 cm-1

13. DPOE-(H2O)3 Cycle vs. Chain
Exp
Theory
DPOE-(H2O)3
Cycle
Theory
DPOE-(H2O)3
Chain
Add Structures
Wavenumber (cm-1)

14. Hamiltonian Matrices
DPOE-(H2O)3
Cycle
Exp
Full Model
Intra + Fermi
Wavenumber (cm-1)
1.92 Å
1.82 Å
2.02 Å
2.22 Å
2.54 Å

15. Hamiltonian Matrices DPOE-(H2O)3 Cycle Exp Full Model Bz-(H2O)3
Intra + Fermi
Wavenumber (cm-1)
1.92 Å
Lowest Frequencies associated with waters?
1.82 Å
2.02 Å
2.22 Å
2.54 Å

16. DPOE-(H2O)4 Exp Full Model Intra + Fermi 1.79 Å 1.74 Å Intra Only
1.82 Å
1.73 Å
2.04 Å
2.65 Å
Wavenumber (cm-1)

17. DPOE-(H2O)4 Exp Full Model Intra + Fermi 1.79 Å 1.74 Å Intra Only
1.82 Å
1.73 Å
2.04 Å
2.65 Å
Wavenumber (cm-1)

18. DPOE-(H2O)n Changes in Site Frequencies

19. Onto TCP-(H2O)n

20. Hamiltonian Matrices
TCP-H2O
TCP-W1
Exp
Full Model
H2O
Wavenumber (cm-1)
Shifts: 61, 44 cm-1

21. Hamiltonian Matrices TCP-(H2O)2 Exp Full Model Intra + Fermi
Wavenumber (cm-1)
The pure H2O dimer H-Bond distance is 1.93 at this level of theory. DPOE-W2 was 1.82.
1.83 Å
H-bond distances
(H2O)2: 1.92 Å
DPOE-(H2O)2: 1.82 Å

22. Two candidate structures:
Clockwise cycle (CW) and
Counterclockwise cycle (CCW)
TCP-(H2O)3 CCW
Exp
Full Model
1.89 Å
Intra + Fermi
1.71 Å
2.02 Å
Wavenumber (cm-1)
Hamiltonian Matrices

23. Two candidate structures: Clockwise cycle (CW) and
Counterclockwise cycle (CCW)
TCP-(H2O)3 CCW
Exp
Full Model
1.89 Å
Intra + Fermi
1.71 Å
2.02 Å
Wavenumber (cm-1)
Hamiltonian Matrices
Add a picture of it sticking in the middle.

24. Two candidate structures: Clockwise cycle (CW) and
Counterclockwise cycle (CCW)
TCP-(H2O)3 CCW
Exp
Full Model
View from top
Intra + Fermi
Wavenumber (cm-1)
Hamiltonian Matrices
Add a picture of it sticking in the middle.
1.71 Å
1.89 Å
2.02 Å

25. TCP-(H2O)4 Candidate StructuresCW Up CW
Down
CCW Up
CCW
Down
Hard to tell these apart, but the “down ones” have a peak near 3700 cm-1 that looks off. Telling the up ones apart is difficult, but they seem less incorrectly shifted up for the CCW up. Looks more clear when you zoom in.
All sort of miss the cm-1 region disappointingly at this level of approximation.

26. TCP-(H2O)4 Candidate Structures
Exp
CCW Up
CW Up
CCW Down
Hard to tell these apart, but the “down ones” have a peak near 3700 cm-1 that looks off. Telling the up ones apart is difficult, but they seem less incorrectly shifted up for the CCW up. Looks more clear when you zoom in.
All sort of miss the cm-1 region disappointingly at this level of approximation.
CW Down
Wavenumber (cm-1)

27. TCP-(H2O)4 CCW Up Exp Full Model Intra + Fermi 1.79 Å 1.72 Å 1.76 Å
1.83 Å
Stretches are quite strongly coupled. Perhaps the Fermi coupling is overestimated when I use the simple 45.3 coupling. Will work on computing it from cubic force constants.
Hard to fit matrices in
Intra Only
Wavenumber (cm-1)

28. TCP-(H2O)4 CCW Up Exp Full Model Intra + Fermi 1.79 Å 1.72 Å 1.76 Å
1.83 Å
Stretches are quite strongly coupled. Perhaps the Fermi coupling is overestimated when I use the simple 45.3 coupling. Will work on computing it from cubic force constants.
Hard to fit matrices in
Intra Only
Wavenumber (cm-1)

29. TCP-(H2O)5 CW Exp Full Model Intra + Fermi Intra Only
CW and CCW are similar but CW fits the intensity profile in the low frequency region better. Had a hard time fitting the bond lengths in on this one.
Hard to fit matrices in
Intra Only
Wavenumber (cm-1)

30. TCP-(H2O)5 CW Exp Full Model Intra + Fermi Intra Only
CW and CCW are similar but CW fits the intensity profile in the low frequency region better. Had a hard time fitting the bond lengths in on this one.
Hard to fit matrices in
Intra Only
Wavenumber (cm-1)

31. TCP-(H2O)n Changes in Site Frequencies

32. Summary
Binding to the phenoxy O atom in DPOE can lead to larger shifts in frequency than binding to the phenyl ring in Bz
The aromatic interaction with TCP and water is about the same strength as with Bz
In some clusters we see half of a piH-bond

33. Acknowledgements
Ned Sibert
Patrick Walsh
Britta Johnson
Funding: NSF