1. Resonant SFG Line Shapes on Single Crystal Surfaces Scott K. Shaw, A. Laguchev, D. Dlott, A. Gewirth Department of Chemistry University of Illinois at Urbana-Champaign 63rd OSU International Symposium on Molecular Spectroscopy Friday, June 20 th 2008 - Columbus, Ohio

2. SFG spectra can reflect simple or complex line shapes Visual interpretation and fitting analysis can be difficult How can we predict/control a desired amount of derivative phase behavior? Schultz, Z.D. JACS. 2005, 127,(45). Shaw, S.K. J Electroanal Chem. 2007, 609, (2). Complex SFG Spectra H2OH2O H2OH2O D2OD2O Air

3. A non-linear, second order, optical process Broad Band IR pulse covers ~ 200 cm -1 window IR combines with narrowband visible pulse at interface Sum frequency photons generated at break in symmetry Sensitive to relative orientation of the vibrational transition 22  1+2 Surface + - + - + - + - + - + - + - + - + - + - + - + - + - + - + - 11 SFG Characteristics

4. 800 nm Vis femtosecond laser 1 kHz, 120 fs 2.0 mJ, 800 nm IR OPA Fabry-Perot étalon spectrograph CCD short pass filter ps vis BB IR sample delay SFG Cartoon of optics layout for BB-SFG J. A. Carter. J Phys Chem A. 2008, 112(16). A non-linear, second order, optical process Broad Band IR pulse covers ~ 200 cm -1 window IR combines with narrowband visible pulse at interface Sum frequency photons generated at break in symmetry Sensitive to relative orientation of the vibrational transition

5. Parameters of resonant transitions are extracted by fitting SFG signal to the equation: Gaussian IR profile Contribution from resonant transitions Non-resonant background Phase factor SFG Characteristics

6. Energy of Incident Radiation Substrate Material Angle of Radiation Incidence Media above sample (solvent) Applied Potential Azimuthal Rotation Temporal Overlap Top: Octadecanethiol on Au in 532 and 1064 nm radiation Bottom: Octadecanethiol on Ag in 532 and 1064 nm radiation Potterton. Bain. J. Electroanal Chem. (409) 1996. SFG Characteristics Varying magnitude of X NR is directly related to changing resonant line shapes

7. Yeganeh et al. have reported varying line shape as a function of rotation They report both non-resonant and resonant intensity changes What are possible sources of resonant intensity change? What is phase term doing? SFG Characteristics Above: single CH 3 resonance from alkanethiol on Au(111) Left: (top) changing resonant intensity and (bottom) changing non-resonant intensity with rotation Yeganeh. Phys Rev Lett. 74(10) 1995. Resonant Non-resonant

8. 1. Use BB-IR SFG to examine a single vibrational transition – Cyanobenzenethiol on Ag Single crystals 2. Examine changes in SFG spectra with sample rotation 3. Explain this dependence Experimental Set-up

9. Rotation of the sample induced drastic changes in SFG signal line shape Non-resonant and phase terms show periodic oscillations Vibrational Wavenumber (cm -1 ) SFG Intensity (A.U.) 000 degrees 050 degrees 040 degrees 030 degrees 020 degrees 010 degrees SFG Anisotropy Data Ag (111)

10. Vibrational Wavenumber (cm -1 ) SFG Intensity (A.U.) 000 degrees 100 degrees 080 degrees 060 degrees 040 degrees 020 degrees SFG Anisotropy Data Ag(110) Rotation of the sample induced drastic changes in SFG signal line shape Non-resonant and phase terms show periodic oscillations

11. Azimuthal Rotation (degrees) Phase (  ) Phase and non-resonant parameters for thiolated faces of Ag Three-fold and two-fold symmetry patterns Similarities to SHG – red lines are fits to equation: Bilger, C. Pettinger B. Chem. Phys. Lett. 1998, 294, (4,5). SFG Anisotropy Data

12. Overlay of non-resonant SFG with SHG for bare surfaces Clear resemblance of (111) face More complicated in (110) face… (reconstruction and (100) oxides) Comparison to SHG Response Azimuthal Rotation (degrees) Relative SFG Intensity SFG and SHG response for (111) surface SFG and SHG response for (110) surface Bilger, C. Pettinger B. Chem. Phys. Lett. 1998, 294, (4,5).Georgiadis, R. Richmond G.L. J. Phys. Chem. 1991, 95, (7). SHG of Ag(111) (+) SFG of Ag(111) ( ) Dashed line is fit to equation SHG of Au(110) (O) SFG of Ag(110) ( )

13. As visible beam is delayed, less sampling of the NR response is up-converted to SFG Delay of Visible Pulse (ps) SFG Intensity -0.50.00.51.01.52.0 -0.5 0.0 0.5 1.0 amplitude (arb) P IR NR (t) P IR R (t) ps vis at different temporal positions Time Delay Scheme for BB-SFG Temporal Delay: Scheme and Effects SFG response as function of vis beam delay J. A. Carter. J Phys Chem A. 2008, 112(16).

14. Lower non-resonant contribution eliminates phase term -0.50.00.51.01.52.0 -0.5 0.0 0.5 1.0 amplitude (arb) P IR NR (t) P IR R (t) ps vis at different temporal positions Time Delay Scheme for BB-SFG Temporal Delay: Scheme and Effects J. A. Carter. J Phys Chem A. 2008, 112(16).

15. CBT decorated Ag surfaces as a function of temporal overlap Constant azimuthal angle maintained Drastic changes in resonant line shape Decreasing intensity of non-resonant term Vibrational Wavenumber (cm -1 ) Relative SFG Intensity No delay ~ 1.5 ps delay ~ 3.0 ps delay No delay ~ 1.9 ps delay ~ 3.7 ps delay Temporal Delay Data Ag (111) Surface Ag (110) Surface

16. Rotational data with a temporal delay to suppress non-resonant term Line shape changes with respect to rotation are absent Changing line shape is definitely associated with the non resonant term Vibrational Wavenumber (cm -1 ) Relative SFG Intensity Temporal Delay Data Ag (111) Surface Ag (110) Surface

17. SFG from single crystal surfaces is azimuthally dependent Can minimize non-resonant response to simply resonant line shapes Allows more consistent approach to future vibrational SFG studies Will simplify analysis of SFG spectra Explains discrepancies in previous data Conclusions:

18. Jonathan Arambula (synthesis of CBT) Alexi Lagutchev, Dana Dlott, Andrew Gewirth* Mauro Sardela (X-ray work) –DMR 050438 –CHE-06-03675 Air Force Office of Scientific Research –FA9550-06-1-0235 Acknowledgements: