1. 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

2. 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, (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

3. 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+
UV Wavelength (nm)
Bz+-(H2O)n+e-
Bz-(H2O)n

4. 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

5. 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

6. 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)
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

7. 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/ g(2d,p) 7

8. 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/ g(2d,p) 8

9. 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/ g(2d,p) 9

10. 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 (95+50=145) and put in single line. 3
OH Bend
1/2 4
M06-2X/ g(2d,p) 10

11. 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/ g(2d,p) 11

12. 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/ g(2d,p) 12

13. 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/ g(2d,p) 13

14. 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/ g(2d,p) 14

15. Benzene-(H2O)6 : Perturbation to Hexamer Book3
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/ g(2d,p) 15

16. 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

17. Scaling Factors
y = x + 550 17

18. Scaling Factor Comparison: Benzene-(H2O)618

19. 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/ g(2d,p) 19

20. 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, (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: /jp502998b

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

22. Scaling Factor Comparison: Benzene-(H2O)422

23. Scaling Factor Comparison: Benzene-(H2O)523