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Columbus, OH, United States

Melnik D.,20 West 18th | Chhantyal-Pun R.,20 West 18th | Miller T.A.,20 West 18th
Journal of Physical Chemistry A | Year: 2010

We demonstrate an experimental method for the accurate measurement of the absorption cross section of transient species, such as organic peroxy radicals in which the concentration of the radicals is determined via the absorption of a stable coproduct that is produced stochiometrically. The requirements for the experimental apparatus, a dual-wavelength cavity ring-down spectrometer, and the chemical protocol for transient species generation are discussed. The capability of this approach is demonstrated by measuring the peak absorption cross section of the ethyl peroxy radical, C2H5O 2, whose value for the Ã←X̃ electronic transition at 7596 cm-1 (λ = 1316.5 nm) is found to be σpEP = 5.29(20) × 10-21 cm2. These present results are compared to those obtained from other methods of measurement of σp EP. Possible random and systematic errors are discussed. © 2010 American Chemical Society.

Chhantyal-Pun R.,20 West 18th | Kline N.D.,20 West 18th | Thomas P.S.,20 West 18th | Miller T.A.,20 West 18th
Journal of Physical Chemistry Letters | Year: 2010

The Ã-X̃ electronic absorption spectrum of β-hydroxyethyl peroxy radical (β-HEP) has been recorded in the NIR by cavity ringdown spectroscopy. The precursor, β-hydroxyethyl radical, is generated by photolysis of 2-iodoethanol and by OH-initiated oxidation of ethene, in both cases followed by addition of O2 to form the peroxy. Although electronic structure calculations predict that 13 conformers of β-HEP exist as minima on the potential energy surface, the experimental spectrum is rationalized in terms of the band origins and vibrational progressions of only the two most stable conformers, G1G2G3 and G1′G2G3. © 2010 American Chemical Society.

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