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Darin J. Ulness, Concordia College

1. Darin J. Ulness, Concordia College. Effects of Hydrogen Bonding on the Ring Stretching Modes of Pyridine and Pyridinium. Darin J. Ulness Department of Chemistry Concordia College Moorhead, MN. 2. Darin J. Ulness, Concordia College. Outline. Introduction II. Experiment

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Darin J. Ulness, Concordia College

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  1. 1 Darin J. Ulness, Concordia College Effects of Hydrogen Bonding on the Ring Stretching Modes of Pyridine and Pyridinium Darin J. Ulness Department of Chemistry Concordia College Moorhead, MN

  2. 2 Darin J. Ulness, Concordia College Outline • Introduction • II. Experiment • Coherent Raman Scattering • III. Hydrogen Bonding • Pyridine systems • Simple model • IV. Prospectus

  3. 3 Darin J. Ulness, Concordia College Spectroscopy Using light to gain information about matter Information Uses of information • In Chemistry • In Biology • In Engineering • Transition frequencies • Dephasing rate constants • Susceptibilities

  4. 4 Material Signal Light field P(t) = P(1) + P(2) + P(3) … P(1) = c(1)E, P(2) = c(2)EE, P(3) = c(3)EEE Darin J. Ulness, Concordia College Nonlinear Optics P= c E Perturbation series approximation

  5. 5 Darin J. Ulness, Concordia College CARS Coherent Anti-Stokes Raman Scattering wCARS w1 w1-w2= wR wCARS= w1 +wR w2 w1 wR

  6. 6 Darin J. Ulness, Concordia College CARS with Noisy Light • I(2)CARS • We need twin noisy beams B and B’. • We also need a narrowband beam, M. • The frequency of B (B’) and M differ by roughly the Raman frequency of the sample. • The I(2)CARS signal has a frequency that is anti-Stokes shifted from that of the noisy beams. I(2)CARS B’ M B

  7. 7 Computer CCD Interferometer Monochromator t Sample B’ B I(2)CARS M Lens Broadband Source (noisy light) Narrowband Source Darin J. Ulness, Concordia College I(2)CARS: Experiment

  8. 8 Darin J. Ulness, Concordia College I(2)CARS: Spectrogram Computer CCD Interferometer Monochromator t Sample B’ B I(2)CARS M Lens Broadband Source Narrowband Source • Signal is dispersed onto the CCD • Entire Spectrum is taken at each delay • 2D data set: the Spectrogram

  9. 9 A Pixel A Pixel B B C Pixel C Darin J. Ulness, Concordia College I(2)CARS: Spectrogram Oscillations: downconversion of Raman frequency. Decay: Lineshape function Dark regions: high intensity Light regions: low intensity

  10. 10 Fourier Transformation X-Marginal Darin J. Ulness, Concordia College I(2)CARS: Data Processing

  11. 11 H O, N O, N Darin J. Ulness, Concordia College Hydrogen Bonding • Interaction between a hydrogen atom and oxygen or nitrogen (or fluorine) • A very weak chemical interaction (bond) • A very strong physical interaction • Exploited extensively in biological systems

  12. 12 N H H C C C C H H C H Darin J. Ulness, Concordia College Pyridine Systems • Why Pyridine • Simple molecule • Important component in many compounds • Biological importance • Strong I(2)CARS signal • H-bond acceptor but not a H-bond donor.

  13. 13 A1 1 990 Darin J. Ulness, Concordia College Pyridine: Normal Modes Ring Breathing A1 Triangle 12 1030

  14. 14 • Neat Pyridine • Two peaks • With H-bond • Three peaks Darin J. Ulness, Concordia College Pyridine and H-bonding

  15. 15 Darin J. Ulness, Concordia College Pyridine and H-bonding • Key Results • Some pyridine is free some is hydrogen bonded • Hydrogen bonding blue-shifts the ring breathing mode • Hydrogen bonding does not shift the triangle mode

  16. 16 Darin J. Ulness, Concordia College Pyridine: Inner Tube Model • Molecular orbitals • Electrostatics • Compare with benzene • Stabilization through p delocalization • H-bonding makes pyridine more “benzene-like”

  17. 17 ≈ Darin J. Ulness, Concordia College Pyridine: Inner Tube Model Electron density for Benzene Electron density for free pyridine + = p e- density Full e- density sp2 e- density Electron density for H-bonded pyridine + = p e- density Full e- density sp2 e- density

  18. 18 3.0 2.8 Formamide 2.6 2.4 4 cm-1 2.2 2.0 1.8 1.6 NormalizedX marginal intensity Water 1.4 8 cm-1 1.2 1.0 0.8 14 cm-1 Acetic Acid 0.6 0.4 0.2 0.0 980 990 1000 1010 1020 1030 1040 -1 Raman wavenumber / cm Darin J. Ulness, Concordia College Pyridine: Test of Model Vary the strength of hydrogen bonding Formamide N-H-N bond ~ 3-4 Kcal/mol Water N-H-O bond ~ 6-7 Kcal/mol Acetic Acid Proton transfer (acid/base)

  19. 19 Darin J. Ulness, Concordia College Pyridine: Peak Broadening

  20. 20 Darin J. Ulness, Concordia College Peak Broadening Models Network model Etc. Thermalized distribution model Fileti, E.E.; Countinho, K.; Malaspina, T.; Canuto, S. Phys. Rev. E. 2003, 67, 061504.

  21. 21 3.0 2.7 2.4 O T = 60 C 2.1 1.8 O T = 40 C Normalized X marginal intensity 1.5 O T = 20 C 1.2 O T = 0 C 0.9 0.6 O T = -20 C 0.3 O T = -40 C 0.0 980 990 1000 1010 1020 1030 1040 -1 Raman wavenumber / cm Darin J. Ulness, Concordia College Pyridine/water Temperature Xpy = 0.55

  22. 22 Darin J. Ulness, Concordia College Pyridine/water Temperature Xpy = 0.55 3.5 Hydrogen Bonded Ring Breathing Mode -1 3.0 Peak width (obs) / cm Triangle Mode 2.5 2.0 1.5 “Free” Pyridine Ring Breathing Mode 1.0 -40 -20 0 20 40 60 O Temperature / C

  23. 23 Triangle Mode 1031.5 1031.0 1030.5 1030.0 Hydrogen Bonded Ring Breathing Mode 1029.5 998 Raman Wavenumber / cm 996 994 “Free” Pyridine Ring Breathing Mode 992 990 988 -40 -20 0 20 40 60 O Temperature / C Darin J. Ulness, Concordia College Pyridine/water Temperature Xpy = 0.55 -1

  24. 24 4.0 3.5 Xpy = 1.0 3.0 Xpy = 0.9 2.5 Xpy = 0.8 Xpy = 0.7 Normalized X marginal Intensity 2.0 1.5 Xpy = 0.6 Xpy = 0.5 1.0 Xpy = 0.4 0.5 Xpy = 0.3 Xpy = 0.2 0.0 980 990 1000 1010 1020 1030 1040 -1 Raman wavenumber / cm Darin J. Ulness, Concordia College Pyridine/Acetic Acid Proton transfer (acid/base reaction)

  25. 25 3.0 2.7 2.4 Xpy = 0.30 2.1 1.8 Xpy = 0.25 Normalized X marginal intensity 1.5 Xpy = 0.20 1.2 Xpy = 0.15 0.9 Xpy = 0.10 0.6 0.3 Xpy = 0.05 0.0 980 990 1000 1010 1020 1030 1040 -1 Raman Wavenumber / cm Darin J. Ulness, Concordia College Pyridine/Acetic Acid

  26. 26 Darin J. Ulness, Concordia College Pyridinium-carboxylate “Electronic” (pKa) study Acetic acid, pKa = 4.77 Difluoroacetic acid, pKa = 1.34 Trichloroacetic acid, pKa = 0.70 Trifluoroacetic acid, pKa = 0.23

  27. 27 Darin J. Ulness, Concordia College Pyridinium-carboxylate Predictions from the inner-tube model • Stronger Acid (low pKa) • Weaker conjugate base • Weaker ion complex • Less “pullback” on the hydrogen • Stronger N-H bond • Better delocalization • Larger blue shift of the ring breathing mode

  28. 28 Darin J. Ulness, Concordia College Pyridinium-Trifluoroacetate

  29. 29 Darin J. Ulness, Concordia College Pyridinium-carboxylate Acid pKa Shift Acetic acid 4.77 13.85 cm-1 Difluoroacetic acid 1.34 17.34 cm-1 Trichloroacetic acid 0.70 18.25 cm-1 Trifluoroacetic acid 0.23 20.35 cm-1 Freely solvated pyridinium 28 cm-1

  30. 30 Darin J. Ulness, Concordia College Prospectus • Summary: • Noisy light provides an alternative method for probing ultrafast dynamics of the condensed phase. • Useful tool for probing hydrogen bonding using “test” molecules. • Simple model useful in understanding hydrogen bonding in pyridine. • Thermalized distribution is likely cause of peak broadening.

  31. 31 Darin J. Ulness, Concordia College Prospectus • Future of noisy light at Concordia: • Other pyridine based molecules • Hydroxymethyl pyridine. • Halo pyridines. • Other nitrogen heterocycles. • A principle goal is to develop an I(2)CARS based microscopy.

  32. 32 Darin J. Ulness, Concordia College Acknowledgements Former Students Jahan Dawlaty: Cornell University, Ph.D. candidate in optical electronics Dan Biebighauser: Vanderbilt University, Ph.D. in mathematics John Gregiore: Cornell University, Ph.D. candidate in physics Duffy Turner: MIT, Ph.D. candidate in physical chemistry Pye Phyo Aung: John’s Hopkins University, Ph.D. candidate in mathematics Tanner Schulz: University of Minnesota, Ph.D. candidate in physics Lindsay Weisel: Michigan State University, Ph.D. candidate in physical chemistry Britt Berger: University of Nevada-Reno, Ph.D. candidate in environmental chemistry Zach Johnson: University of Nevada-Reno, Ph.D. candidate in environmental chemistry Current Students Other Group Members Erik Berg Danny Green Diane Moliva Brady Bjerke Dr. Mark Gealy, Department of Physics Dr. Haiyan Fan, Post-doctoral researcher Funding NSF CAREER Grant CHE-0341087 Henry Dreyfus Teacher/Scholar program Concordia Chemistry Research Fund

  33. Darin J. Ulness, Concordia College

  34. 5 Time resolution on the order of the correlation time, tc Noisy Light Spectrum Frequency Darin J. Ulness, Concordia College Noisy Light: Definition • Broadband • Phase incoherent • Quasi continuous wave

  35. 23 Darin J. Ulness, Concordia College Pyridine and Water

  36. 7 Darin J. Ulness, Concordia College Noisy Light: Alternative • Its cw nature allows precise measurement of transition frequencies. • Its ultrashort noise correlation time offers femtosecond scale time resolution. • It offers a different way to study the lineshaping function. • It is particularly useful for coherent Raman scattering. • Other spectroscopies: photon echo, OKE, FROG, polarization beats…

  37. 8 Noisy Light Spectroscopy Optical coherence theory Perturbation theory: Density operator Darin J. Ulness, Concordia College Theory

  38. 9 Difficulty • The cw nature requires all field action permutations. The light is always on. • The proper treatment of the noise cross-correlates chromophores. Solution • Factorized time correlation (FTC) diagram analysis Darin J. Ulness, Concordia College Theoretical Challenges • Complicated Mathematics • Complicated Physical Interpretation

  39. 10 Messy integration and algebra Construction Rules Evaluation Rules Set of intensity level terms (pre-evaluated) Set of FTC diagrams Set of evaluated intensity level terms easy Physics hard hard Darin J. Ulness, Concordia College Noisy Light Spectroscopy FTC Diagram Analysis

  40. A1 Darin J. Ulness, Concordia College Noisy Light Spectroscopy Utility of FTC Diagrams • Organize lengthy calculations • Error checking • Identification of important terms • Immediate information of about features of spectrograms • Much physical insight that transcends the choice of mathematical model.

  41. A2 a P(t,{ti}) b P(s,{si}) Darin J. Ulness, Concordia College Noisy Light Spectroscopy Example: I(2)CARS • FTC analysis • Each diagram with arrows has a topologically equivalent partner diagram containing only lines: 2:1 dynamic range • Each diagram with arrows has a topologically equivalent partner diagram that has arrows pointing in the opposite direction: signal must be symmetric in t arrow segments: B, B’ correlation t-dependent line segments: B, B or B’,B’ correlation t-independent

  42. 4 Darin J. Ulness, Concordia College Noisy Light Spectroscopy Modern Spectroscopy Frequency Domain Time Domain • Measure Spectra • Examples • IR, UV-VIS, Raman • Material response • Spectrally narrow • Temporally slow • Response to light pulse • Examples • PE, transient abs. • Material response • Spectrally broad • Temporally fast

  43. 4 Darin J. Ulness, Concordia College Noisy Light Spectroscopy Modern Spectroscopy Frequency Domain Time Domain • Measure Spectra • Examples • IR, UV-VIS, Raman • Material response • Spectrally narrow • Temporally slow • Response to light pulse • Examples • PE, transient abs. • Material response • Spectrally broad • Temporally fast

  44. 4 Darin J. Ulness, Concordia College Noisy Light Spectroscopy Modern Spectroscopy Frequency Domain Time Domain • Measure Spectra • Examples • IR, UV-VIS, Raman • Material response • Spectrally narrow • Temporally slow • Response to light pulse • Examples • PE, transient abs. • Material response • Spectrally broad • Temporally fast Is there another useful technique? Noisy light? YES!

  45. A3 A Pixel A Pixel B B C Pixel C Darin J. Ulness, Concordia College Noisy Light Spectroscopy Example: I(2)CARS • The I(2)CARS data shows • 2:1 dynamics range • t symmetry

  46. A4 (a) 0.30 0.25 0.20 0.15 g s 0.10 0.05 0.00 0 1 2 3 4 5 S/N (b) 0.25 0.20 0.15 0 D w s 0.10 0.05 0.00 0 1 2 3 4 5 S/N Darin J. Ulness, Concordia College Noisy Light Spectroscopy

  47. A5 Darin J. Ulness, Concordia College Noisy Light Spectroscopy

  48. A6 Darin J. Ulness, Concordia College Noisy Light Spectroscopy

  49. A7 Darin J. Ulness, Concordia College Noisy Light Spectroscopy - ∆G° Product Favored - ∆H° Exothermic - ∆S° Entropically unfavorable

  50. A8 Darin J. Ulness, Concordia College Noisy Light Spectroscopy c(3)complex = Icomplexc(3)free xfree Icomplex = Ifree at 0.21 mole fraction c(3)complex = 1c(3)free .79 c(3)complex = 3.76c(3)free

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