1. Finding optimal ion-solvent configurations using FTIR For Studying ion association dynamics of thiocyanate salt by 2DIR spectroscopy Maria Gonzalez Office of Science, Science Undergraduate Internship Program Loyola University, New Orleans, LA Stanford Linear Accelerator Center Menlo Park, California August 14, 2008

2. Abstract The ion association and dissociation dynamics in thiocyanate salt solutions will be probed using 2D-IR spectroscopy allowing for the determination of equilibrium association (or dissociation) rate constants of the thyocyanate anion and its counter cation. Thiocyanate’s nitrile stretch, which is sensitive to ionic interactions, was used in revealing the interaction among the thiocyanate ion and the cation in solution. The optimal solution parameters for the thiocyanate salts was determined by a one to one area ratio of the nitrile vibrational frequency of free thiocyanate to the contact ion pair using one dimensional infrared spectroscopy.

3. Infrared &Thiocyante Nitrile Stretch ~ 2100-2240 cm-1 Free thiocyanate ion ~ 2050 cm-1 Contact Ion Pair ~ 2070 cm-1

4. Ultrafast Vibrational Spectroscopy Understanding of the ultrafast structural dynamics of complex molecular systems in solution has been restricted by the fast time scale such processes take place on Vibrational excitations, in contrast to electronic excitations,  produce a negligible perturbation with less energetic IR photons.  don’t change chemical properties of molecules under study. Ultrafast Vibrational spectroscopy  allows study molecular systems under thermal equilibrium conditions.  measures dynamics occurring on fs and ps time scales. v = 0 v = 1 v = 2  Fundamental First overtone Anharmonicity v = 0 v = 1 v = 2 v` = 0 v` = 1 v` = 2 S0S0 S1S1

5. 2DIR Experiments k sig = -k 1 +k 2 +k 3 k1k1 k2k2 k3k3 k1k1 k2k2 k3k3 Sample Monochromator local oscillator MCT Array Detector beam combiner k1k1 k2k2 k3k3 k sig E sig - 2DIR experiment is performed with multiple pulse sequences. - Time-delayed three IR pulses are focused onto the sample in a noncollinear geometry. - Emitted signal is overlapped with a local oscillator for heterodyne detection. - Heterodyned signal is dispersed through a monochromator and is frequency-resolved. - Dual scan method with two different pulse sequences is used to measure purely absorptive part of signal. Laser Phys. Lett., 4, 704 (2007)

6. AB Chemical Exchange A  A species A - frequency  A B  B species B - frequency  B A and B give diagonal peaks 0-1 region only mm  B A ABAB Consider one diagram for the 0-1 region  AA  BB ABAB TwTw 1 st interaction -  A Last interaction -  B Off-diagonal mm  B A ABAB  BB  AA B AB A TwTw B AB A 1 st interaction -  B Last interaction -  A Off-diagonal mm  B A ABAB

7. AB Chemical Exchange mm  B A ABAB ABAB - Combining AB and B AB A - Including the 1-2 pathways Off-diagonal peaks in each block grow in as T w is increased. The T w dependent growth of the off-diagonal peaks in each block gives the chemical exchange rate.

8. Two-state chemical exchange dynamics A B k AB k BA T 1,A,  or,A T 1,B,  or,B Decay FFCF B FFCF A Spectral diffusion

9. Finding Optimal Solution Parameters

10. Thiocyanate SaltsSolventsDielectric Constant Sodium Thiocyanate Lithium Thiocyante Dimethylsulphoxide(26.8ºF) Acetonirile (70° F) Acetone (77° F) Ethyl Ether (68° F) Ethanol (77° F) Methanol (77° F) 47.1 37.5 20.7 4.3 24.3 32.6 Nitrile Stretch = (2100-2240 cm -1 ) Free thiocyanate ion ~ 2050 cm -1 Contact Ion Pair ~ 2070 cm -1 Contact Ion Pair Free Ion

14. Conclusion Optimal solution parameters: –Lithium Thiocyante: 0.040 ±0.002M lithium thiocyanate in diethyl ether with 0.118mols ± 0.001 of lithium chloride –Sodium Thiocyante: 0.060±0.003M sodium thiocyanate in acetonitrile

15. Special Thanks Department of Energy Dr. Steven Rock, Farah Rahbar, & Susan Schultz Dr. Kelly Gaffney Dr. Sugnam Park Minbiao Ji

16. References Suydam, I. T.; Boxer, S. G. Biochemistry 2003, 42, 120 Park, S.; Kwan, K. Laser Phys. Lett., 2007, 705, 710 Zheng, J.: Kwan, K; Fayer, M.D. Acc. Chem. Res. 2007, 76, 78 Marcus, Y., Ion Solvation, New York, Wiley, 1985, in Chapter 3 “Infra-red Spectra and Solvation of Ions in Dipolar Protic Solvents” Butcher, P.N; Cotter, D. The elements of Nonlinear Optics, Cambridge University Press: Cambridge, U.K., 1990, 50-78 Landolt-Börnstein, Group IV Physical Chemistry, Springer Berlin Heidelberg Press: Berlin, Germany, 2008, Volume 17, 269-270Landolt-Börnstein, Group IV Physical Chemistry