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Victoria P. Barber and Josh J. Newby TK14 Department of Chemistry and Biochemistry, Swarthmore College Swarthmore, PA 19081 Spectroscopic characterization of a natural product: anethole
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Motivation Natural products Low amplitude motions Complete the spectroscopy
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Early work (Grassian et al.) Syn Anti R2PI Grassian et al. J. Phys. Chem. 1989, 93 3470-3474
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Cools gas phase molecules to effective temperatures of a few degrees Kelvin Boltzmann distribution of conformations Collisional cooling Jet-cooled spectroscopy Buffer gas A A A B B BB B B A A B A AA B B B B B A A B B A A A B B B B B A A B B Isolated, cold molecules High Pressure (1 bar)Low Pressure (10 -7 bar)
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Excited Fluorescence spectroscopy Ground 1.LIF Tune laser, measure total fluorescence Excited state vibrations 2.SVLF Park laser, disperse fluoresce Ground state vibrations
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LIF spectrum of anethole
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SynAnti Bands separated by 70 cm -1
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Origin SVLF spectra Two conformers confirmed SVLF Anti Syn
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Computation AntiSyn (wavenumbers) B3LYP/6-311++G(d,p) Grassian assignments confirmed
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Detect total fluorescence Probe (20 Hz) Conformer A(S 0, ZPL) HB (10 Hz) UVHB UV Hole-burn laser fixed UV probe laser tuned UVHB Hole-burning of anethole (Purdue) A (S 1 ) Syn Anti
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(a)Warm conditions (b) Cold Conditions 10 psi 30 psi v = 0 v = 1 v = 0 v = 1 v = 2 v = 3 S1S1 S0S0 Pressure study (a) (b)
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Origin SVLF spectra (Purdue) Anti Syn
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Syn SVLF (in plane) Simple false origin SVLF of in plane IVR
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Syn SVLF (out of plane) Significant Duschinsky mixing of out of plane modes
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Syn Hot bands SVLF Identical absolute frequency implies same upper state
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Anti SVLF
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FCF of ν 39 Conformations differ in displacement
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MOs of anethole MeO orientation tweaks MO geometry
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Syn/Anti Isomerization
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Isomerization
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(a)Warm conditions (b) Cold Conditions 10 psi 30 psi v = 0 v = 1 v = 0 v = 1 v = 2 v = 3 S1S1 S0S0 Pressure study (a) (b)
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SVLF spectra of Syn origin and Syn+58 Similar structure New low frequency bands Implies VDW cluster Syn 0 0 Syn +58
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SVLF spectra of Syn origin and Anti+51 Similar structure New low frequency bands Implies VDW cluster Anti 0 0 Anti +51
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LIF of water clusters ‘Neat’ sample has water clusters! Neat +H 2 O
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Spontaneous Emulsion (Ouzo Effect) Ouzo Absinthe
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Styrene : water Origin shift n=1 => 21.5 cm -1 n=2 => 46.5 cm -1 anisole : water Origin shift n=1 => 118 cm -1 n=2 => 107 cm -1 Water cluster comparison Reimann et al. J. Chem. Phys. 117(19) 2002 8805 Mahmoud et al. Chem. Phys. Lett. 356 2002 91
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LAM Comparison Syn Anti
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Two conformations (syn/anti) Similar with key differences (ν 63, ν 39 ) Styrene like vibrational characteristics OMe is sneaks in Readily clusters with water Trimers form without much effort? Key points
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Swarthmore Prof. Thomas A. Stephenson Victoria P. Barber Madeleine Amodio Purdue Prof. Timothy S. Zwier Deepali N. Mehta-Hurt Acknowledgements
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