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Ultraviolet Photodissociation Dynamics of the 3-Cyclohexenyl Radical Michael Lucas, Yanlin Liu, Jasmine Minor, Raquel Bryant, Jingsong Zhang Department of Chemistry University of California, Riverside 69 th International Symposium on Molecular Spectroscopy 6/17/2014
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Photodissociation of Free Radicals Free radicals Open shell Highly reactive Important in many areas of chemistry Combustion, atmospheric, plasma, interstellar Dissociation depends on potential energy surfaces Provide benchmarks for theory
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Cyclohexyenl Radical Cycloalkanes are important component of conventional fuels Cyclohexane model cycloalkane Major producer of benzene Previous Research: cyclohexyl, phenyl What effect does the double bond have on the photochemistry?
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Potential Energy Diagram of c-C 6 H 9 ~ ~ ● ● ● K. Furukawa et al. Int. J. Chem. Kin. 6 (1974) 337 NIST Chemistry WebBook
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High-n Rydberg H-atom Time-of-Flight (HRTOF) H Lyman- Probe 121.6 nm Photolysis Pulsed Valve Rydberg Probe 366.2 nm Detector Skimmer 193 nm H transitions 1 2 nH+H+ H (n) H (2 2 P) 121.6 nm Lyman- 366.2 nm K. Welge and co-workers, J Chem Phys 92 (1990) 7027 3-chlorocyclohexene 3-bromocyclohexene
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Production of Cyclohexenyl Radical Beam 121.6-nm VUV photoionization mass spectrometry Net mass spectrum: 193-nm radical generation radiation on minus off Radical production Precursor depletion
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H-atom TOF Spectra check precursors
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H-atom Product Action Spectrum compare with absorption spectrum R. Schuler et al. Chem. Phys. Lett. 27 (1974) 369; D. Pratt et al. J. Am. Chem. Soc. 96 (1974) 5588
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CM Product Translational Energy Distribution
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Average E T Release
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H-atom Product Angular Distribution E v Major: β ~ 0 Isotropic distribution Dissociation time slower than 1 rotational period (ps) Minor: β < 0 Anisotropic distribution Dissociation time faster than 1 rotational period *
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H-atom Product Angular Distribution Major: β ~ 0 Isotropic distribution Dissociation time slower than 1 rotational period (ps) E v Minor: β < 0 Anisotropic distribution Dissociation time faster than 1 rotational period
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Photodissociation Mechanism ~ ~ ● ● ● Repulsive dissociation I.C. Unimolecular Dissociation
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Summary UV photodissociation dynamics of cyclohexenyl was studied in 232-262 nm for the first time Observed: cyclohexenyl → cyclohexadiene + H Modest translational energy release, f T ~ 0.15 Two components Major: Isotropic distribution, β ~ 0 Dissociation mechanism: internal conversion from excited electronic state followed by unimolecular dissociation on ground electronic state Minor: Anisotropic distribution, β < 0 Dissociation mechanism: direct dissociation from excite state or repulsive part of ground state
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Comparison With Cyclohexyl
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Moderate translational energy release Two component Major Isotropic distribution Statistical distribution Hot radical dissociation mechanism Minor Anisotropic distribution, β < 0 Repulsive dissociation mechanism Large translational energy release Anisotropic distribution, β > 0 Non-statistical distribution Dissociation mechanism: direct dissociation from the excited state and/or on the repulsive part of the ground state (possibly via conical intersection). CyclohexenylCyclohexyl
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Acknowledgements Prof. Jingsong Zhang Yanlin Liu Jasmine Minor Raquel Bryant Zhang Group
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