Presentation on theme: "OBSERVATION OF THE A-X ELECTRONIC TRANSITION OF C 6 -C 10 PEROXY RADICALS Neal D. Kline and Terry A. Miller Laser Spectroscopy Facility The Ohio State."— Presentation transcript:
OBSERVATION OF THE A-X ELECTRONIC TRANSITION OF C 6 -C 10 PEROXY RADICALS Neal D. Kline and Terry A. Miller Laser Spectroscopy Facility The Ohio State University ~ ~
Motivation for Study of Peroxy Radicals Key combustion intermediates Atmospheric chemistry: lead to formation and destruction of ozone RO 2 OH R’CHO RO RH RO 2 NO 2 RONO 2 HO 2 CO CO 2 R’C(O)O 2 PAN ROOH O2O2 NO 2 HO 2 NO h OH NO 2 NO NO 2 h OH O2O2 O2O2 NO 2 NO Isomerisation Multistep h NO 2 O 2 1. Lightfoot et. al. Atmos. Envir. 26A, 1805. 1
C 6 -C 10 Peroxy Radicals Gasoline mixtures contain a mixture of hydrocarbons: parrafins, olefins, and aromatics. Larger chain hydrocarbons(>C 5 ) make up a significant portion of gasoline mixtures; heptane and 2,2,4-trimethyl pentane (isooctane) are standards for octane rating scale with ratings of 0 and 100, respectively. Picture of refineries
Low-Lying Electronic Transitions of Peroxy Radicals B−X transition: Strong (c.f. O 2 : B 3 Σ u − ← X 3 Σ g − ) Located in UV: ca. 49000 cm -1 Repulsive → little structural information, poor selectivity HOMO-1 HOMO SOMO O. J. Nielsen and T. J. Wallington, in Peroxyl Radicals, (John Wiley and Sons, New York, 1997), pp. 72-73. ~~ Jafri, J. A, and D. H. Phillips. J. Am. Chem. Soc. 112 (1990) 2586. R O–O X ~ A ~ B ~
Low-Lying Electronic Transitions of Peroxy Radicals A−X transition: Weak (c.f. O 2 : a 1 Δ g ← X 3 Σ g − ) Located in NIR: ca. 7500 cm -1 Bound → resolved vibrational structure HOMO-1 HOMO SOMO Chung et al. J. Chem. Phys. 127 (2007) 044311. ~~ Jafri, J. A, and D. H. Phillips. J. Am. Chem. Soc. 112 (1990) 2586. R O–O X ~ A ~ B ~
Assignment of Spectra To assign spectra for peroxy radicals, typically perform A-X origin calculations using G2 level of theory. Frequency calculations with DFT methods. Larger straight chain peroxy radicals are computationally expensive to calculate at the G2 level of theory. Assignments were deduced from spectral/structural relationships that have been determined from prior studies, and previous experience with assigning peroxy radical spectra ~ ~
Assignment of Isooctyl Peroxy A A’ B’B C’ BandAssignmentFrequency A Origin secondary isomer7503 A’ Origin tertiary isomer7804 B’COO bend8230 B-OO Stretch8460 C'-OO Stretch8734 1. Glover, B. and Miller, T.A. J. Phys. Chem. A., 2005, 109, 11191.
Conclusions Conclusions: A-X spectra of C 6 -C 10 straight chain peroxy radicals and isooctyl peroxy have been obtained and analyzed. Assignments were made by examining the spectral/structural relationships of peroxy radicals.
Acknowledgments Prof. Terry Miller Miller group: Funding: -US Department of Energy (DOE) -Dr. Dmitry Melnik -Dr. Mourad Roudjane -Rabi Chhantyal-Pun -Terrance Codd -Meng Huang
Assignment of Isooctyl Peroxy Peroxy Radical OriginCOO Bend -OO Stretch tert- isooctyl Peroxy780482308734 Heptyl Peroxy7503-8460 Octyl Peroxy7596-8513 Nonyl Peroxy7597-8513 Decyl Peroxy7573-8505 A A’ B’B C’