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

Vibrational energy in reaction dynamics Polanyi rules

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

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

H-Abstraction reaction of Br Endothermic reaction H-abstraction reaction of Br is a good system to test the effect of vibrational mediation

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

Experimental setup

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

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

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

Experimental setup for HBr detection

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

Acknowledgements Prof. F. Fleming Crim The Crim group Michael Shalowski