1. Experimental Measurement of the Induced Dipole Moment of an Isolated Molecule in Its Ground and Electronically Excited States. Indole and Indole-H2O.*
CHEOLHWA KANG and DAVID PRATT, University of Pittsburgh,and TIMOTHY KORTER, Syracuse University
*Work supported by NSF (CHE ).

2. Solvent Reorganization in Indole-H2O

3. High Resolution Spectrometer

4. Indole-Water Complex Experimental B subband A subband 35097.5
cm-1
Indole-Water Complex

5. Fit

6. Internal Rotation S1 B A S0 O a H ρ ↔ q q θ ρ ~ cos θ
ΔA (or ΔB, ΔC) = F •ωg(2) • ρ2g (g = a,b,c)
ρ ↔ q
complex a axis
attached rotor axis θ
ρ ~ cos θ a H
Internal Rotation O

7. Inertial Parameters Indole A, MHz 3877.8 (2) 2064.2 (2) 2062.5 (1)
Indole-H2O
A, MHz (2) (2) (1)
B, MHz (1) (3) (1)
C, MHz (1) (2) (1)
ΔI, amu Å
A subband B subband
A, MHz (2) (2) (2)
B, MHz (1) (3) (1)
C, MHz (1) (2) (1)
ΔI, amu Å

8. Solvent Reorganizationθ
θ = 0 ±15 º
Solvent Reorganization
θ = 55 ± 15º
h ν
The axis about which the water is rotating is different in the S1 state.

9. Stark Experiments on Indole and Indole-H2O
Determine the permanent electric dipole moment of the
isolated molecule in both electronic states.
water complex in both electronic states.
Determine the induced electric dipole moment of the

10. Stark Electrodes and Collection Optics

11. Stark Effect Spectra of Indole
0 V/cm
348 V/cm
696 V/cm
1303 V/cm
1740 V/cm
2606 V/cm
2.24 cm-1

12. Stark Fits 509 V/cm 1018 V/cm 2036 V/cm 0.08 cm-1 35231.57

13. Dipole Moments of Indolea b
μ (S0) = D
μ (S1) = D θD
θD = (6)
θD = (4)
Dipole Moments of Indole

14. Stark Effect Spectra of Indole-H2O
509 V/cm
1018 V/cm
2036 V/cm
0.10 cm-1
cm-1

15. Dipole Moments of Indole-Water
h ν a H θD μ″ μ′
θD = + 13 º
θD = - 16 º
μ″ = 4.4 D
μ′ = 4.0 D
Rcom = Å
Rcom = 4.602Å

16. μtotal = μ indole + μwater + μ induced
Dipole Moments μa μb
μtot
Indole S0 S1
1.376 (8)
1.40 (1)
1.963 (13)
1.556 (8)
1.01 (1)
1.856 (13) +
Water
1.85
Indole - Water
4.20 (6)
1.2 (3)
4.4 (3)
3.90 (8)
0.9 (3)
4.0 (3) ≠
Not simple vector sum
μtotal = μ indole + μwater + μ induced
- Need induced dipole moment

17. Induced Dipole Moments≈
Induced Dipole Moments + α
μ,Θ
α,Θ
α = polarizability
Θ = quadrupole moment

18. Dipole Moments
Calculated
Experimental
4.11
1.15
4.27
3.54
0.66
3.60
without Θ
4.24
1.18
4.40
3.81
0.77
3.89
with Θ μa
4.20 (6) S0 μb
1.2 (3)
μtot
4.4 (1) μa
3.90 (8) S1 μb
0.9 (3)
μtot
4.0 (2)
μI (S0) = 0.7 D, μI (S1) = 0.5 D

19. Vector Model N N Water dipole Indole dipole Induced dipole h ν a a H O

20. Summary Acknowledgements
High resolution electronic spectroscopy in the gas phase has been used to determine the magnitude and orientation of the induced dipole moment that is produced when an indole molecule in its ground S0 and electronically excited S1 states is polarized by the attachment of a water molecule in the hydrogen bonded complex indole-H2O.
Acknowledgements
We thank Dr. John Kuehne and Mr. Val Kagan for technical assistance.
This work has been supported by NSF (CHE )