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Vibrationally Driven Hydrogen Abstraction Reaction of Bromine Radical in Solution Jae Yoon Shin, Michael A. Shalowski, F. Fleming Crim OSU International Symposium on Molecular Spectroscopy June 21, 2013
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Vibrational energy in reaction dynamics Polanyi rules
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Vibrationally driven chemistry in gas phase Yoon, S; Holiday, R.; Crim, F. J. Phys. Chem. B 2005, 109, 8388 Reaction of Cl with CH 3 D in the gas phase Vibrational energy in either the C-H or C-D stretch selectively enhances formation of either HCl or DCl
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Bimolecular reaction in solution phase Sheps, L.; Crowther, A.; Carrier, S.; Crim, F. J. Phys. Chem. A 2006, 110, 3087 Reaction of Cl with n-pentane in the solution phase Cl radical forms a charge transfer (CT) complex with solvent H-Cl vibrational frequency at 3600 nm
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H-Abstraction reaction of Br Endothermic reaction H-abstraction reaction of Br is a good system to test the effect of vibrational mediation
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Br + DMSO reaction scheme CHBr 3 (CH 3 ) 2 SOHBrBr Photolyzing CHBr 3 with 266 nm Exciting C-H overtone with 1700 nm (5882 cm -1 ); ∆H reaction = 2269 cm -1 Monitoring CT complex of Br-DMSO with 400 nm 0.06 M CHBr 3 solution in dimethyl sulfoxide (DMSO) CH 2 SOCH 3
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Experimental setup
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Br + DMSO Two-beam signal 266 nm pump 400 nm probe - Formation of CT complex - Loss of CT complex; geminate recombination of Br 1700 nm pump 400 nm probe - No CT complex formed without photolysis Two-beam signal UVIR UVIR
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Br + DMSO Three-beam signal Difference signal (Three-beam signal − two-beam signals) - Both pump beams are overlapped in time - Formation of CT complex - Loss of CT complex; geminate recombination of Br and reaction of Br with H Loss of Br from; - vibrational predissociation of Br from CT complex and recombination - reaction of Br forming HBr 400 and 1700 nm pump 400 nm probe Three-beam signal − two-beam signals
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Br + DMSO IR pump wavelength dependence of difference signals Absorption spectrum of neat DMSO Difference signals Large negative offset in difference signal when IR pump wavelength is on-resonance with C-H overtone Monitoring formation of HBr product with 4000 nm light can be a direct evidence
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Experimental setup for HBr detection
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Test experiment Revisited reaction of Cl with n-pentane HCl detection with array detector Time trace at 2810 cm -1 - Confirmed previous data - Better sensitivity - Ready for HBr detection in Br + DMSO reaction ΔAΔA
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Acknowledgements Prof. F. Fleming Crim The Crim group Michael Shalowski
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