Spectroscopic studies of the $\tilde{A}$Ã–$\tilde{X}$X̃ electronic spectrum of the β-hydroxyethylperoxy radical: Structure and dynamics

Chen, Ming-Wei; Just, Gabriel M. P.; Codd, Terrance J.; Miller, Terry A.

doi:10.1063/1.3656835

Cited by 9 publications

(4 citation statements)

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“…The congestion of the phenylperoxy spectrum may be significantly reduced by the application of jet-expansion cooling techniques. Miller and co-workers have shown that cold peroxy radicals can be produced using O 2 addition reactions in an electric discharge slit expansion. − In the recent past we have used the discharge slit expansion technique to record rotationally resolved spectra for the 1 2 B 1 –X̃ 2 A 1 transition of the phenyl radical . In the present study we used the same system to examine phenylperoxy.…”

Section: Introductionmentioning

confidence: 99%

Structure in the Visible Absorption Bands of Jet-Cooled Phenylperoxy Radicals

et al. 2013

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The visible absorption bands of the phenylperoxy radical in the gas phase have been investigated using cavity ring-down spectroscopy. Jet-cooling was used to reduce the spectral congestion. Structured spectra spanning the range from 17 500 to 19 000 cm–1 are reported for the first time. Analyses of these data have been guided by the results from time-dependent density functional calculations. The observed spectrum was found to be dominated by the bands of the B̃2A″–X̃2A″ transition. An analysis of the rotational contour for the origin band yielded a homogeneous line width of 2.2 cm–1, corresponding to a decay rate of 4.1 × 1011 s–1. The results provide a rationale for the lack of structure in room temperature spectra that have been previously attributed to phenylperoxy. They also indicate that the lower energy region of the spectrum may show resolvable structure at room temperature. If so, this would provide a more definitive signature for monitoring phenylperoxy in kinetic measurements.

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Section: Introductionmentioning

confidence: 99%

Structure in the Visible Absorption Bands of Jet-Cooled Phenylperoxy Radicals

et al. 2013

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“…Within the context of the atmospheric decomposition of alkanes and alkenes, the importance of considering the effect of intramolecular hydrogen bonding on certain reactions in the oxidation mechanism have long been known. Several studies have focused on hydroperoxyalkylperoxy, hydroxyalkylperoxy, − and hydroxyalkoxy radicals. ,,− A review by Zádor et al provides an extensive discussion of oxygenated alkyl radicals, which includes each of these three groups of molecules . Dibble has reported on the role that hydroxyalkoxy radicals play in the atmospheric decomposition of several natural VOCs, including isoprene, α - and β-pinene, and alkenes. , Vereecken and Peeters in their study on oxygenated hydrocarbons reported the impact that intramolecular H-bonding could have on reactant and transition state stabilities for systems with the OH group residing both inside and outside the transition state ring .…”

Section: Introductionmentioning

confidence: 99%

Hydroxyalkoxy Radicals: Importance of Intramolecular Hydrogen Bonding on Chain Branching Reactions in the Combustion and Atmospheric Decomposition of Hydrocarbons

Davis

Francisco

2014

J. Phys. Chem. A

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During both the atmospheric oxidation and combustion of volatile organic compounds, sequential addition of oxygen can lead to compounds that contain multiple hydrogen-bonding sites. The presence of two or more of these sites on a hydrocarbon introduces the possibility of intramolecular H-bonding, which can have a stabilizing effect on the reactants, products, and transition states of subsequent reactions. The present work compares the absolute energies of two sets of conformations, those that contain intramolecular H-bonds and those that lack intramolecular H-bonds, for each reactant, product, and transition state species in the 1,2 through 1,7 H-migrations and Cα-Cβ, Cα-H, and Cα-OH-bond scission reactions in the n-hydroxyeth-1-oxy through n-hydroxyhex-1-oxy radicals, for n ranging from 1 to 6. The difference in energy between the two conformations represents the balance between the stabilizing effects of H-bonds and the steric cost of bringing the two H-bonding sites together. The effect of intramolecular H-bonding and the OH group is assessed by comparing the net intramolecular H-bond stabilization energies, the reaction enthalpies, and barrier heights of the n-hydroxyalkoxy radical reactions with the corresponding alkoxy radicals values. The results suggest that there is a complex dependence on the location of the two H-bonding groups, the location of the abstraction or bond scission, and the shape of the transition state that dictates the extent to which intramolecular H-bonding effects the relative importance of H-migration and bond scission reactions for each n-hydroxyalkoxy radical. These findings have important implications for future studies on hydrocarbons with multiple H-bonding sites.

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“…This transition is a bound-to-bound n ← n transition localized on the O–O group, with the exact position and structure dependent on the structure and functional groups of the peroxy radical. They have reported detection of the Ã ← X̃ transition for two hydroxy-peroxy radicals, the 2,1-hydroxy-ethyl-peroxy and 2,1-hydroxy-propyl-peroxy radicals. − These authors have performed thorough investigations of the bands arising both from progressions of Franck-Condon active modes and from low-lying conformers that have significant populations.…”

Section: Introductionmentioning

confidence: 99%

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

et al. 2013

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We report vibrational and electronic spectra of the hydroxy-methylperoxy radical (HOCH 2 OO • or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO 2• , and formaldehyde, HCHO. The ν 1 vibrational (OH stretch) spectrum and the A ̃← X ̃electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO 2• . Free radical reactions were initiated by pulsed laser photolysis (PLP) of Cl 2 in the presence of HCHO and O 2 in a flow reactor at 300−330 Torr and 295 K. IR-CRDS spectra were measured in mid-IR and near-IR regions over the ranges 3525−3700 cm −1 (ν 1 ) and 7250−7800 cm −1 (A ̃← X ) respectively, at a delay time 100 μs after photolysis. The ν 1 spectrum had an origin at 3622 cm −1 and exhibited partially resolved P-and R-branch contours and a small Q-branch. At these short delay times, spectral interference from HOOH and HCOOH was minimal and could be subtracted. From B3LYP/6-31+G(d,p) calculations, we found that the anharmonic vibrational frequency and band contour predicted for the lowest energy conformer, HMP-A, were in good agreement with the observed spectrum. In the near-IR, we observed four well spaced vibronic bands, each with partially resolved rotational contours. We assigned the apparent origin of the A ̃← X ̃electronic spectrum of HMP at 7389 cm −1 and two bands to the blue to a progression in ν 15 ′, the lowest torsional mode of the A ̃state (ν 15 ′ = 171 cm −1 ). The band furthest to the red was assigned as a hot band in ν 15 ″, leading to a ground state torsional frequency of (ν 15 ″ = 122 cm −1 ). We simulated the spectrum using second order vibrational perturbation theory (VPT2) with B3LYP/6-31+G(d,p) calculations at the minimum energy geometries of the HMP-A conformer on the X ̃and A ̃states. The predictions of the electronic origin frequency, torsional frequencies, anharmonicities, and rotational band contours matched the observed spectrum. We investigated the torsional modes more explicitly by computing potential energy surfaces of HMP as a function of the two dihedral angles τ HOCO and τ OOCO . Wave functions and energy levels were calculated on the basis of this potential surface; these results were used to calculate the Franck−Condon factors, which reproduced the vibronic band intensities in the observed electronic spectrum. The transitions that we observed all involved states with wave functions localized on the minimum energy conformer, HMP-A. Our calculations indicated that the observed near-IR spectrum was that of the lowest energy X ̃state conformer HMP-A, but that this conformer is not the lowest energy conformer in the A ̃state, which remains unobserved. We estimated that the energy of this lowest conformer (HMP-B) of the A ̃state is E 0 (A , HMP-B) ≈ 7200 cm −1 , on the basis of the energy difference E 0 (HMP-B) − E 0 (HMP-A) on the A ̃state computed at the B3LYP/6-31+G(d,p) level.

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Spectroscopic studies of the $\tilde{A}$Ã–$\tilde{X}$X̃ electronic spectrum of the β-hydroxyethylperoxy radical: Structure and dynamics

Cited by 9 publications

References 50 publications

Structure in the Visible Absorption Bands of Jet-Cooled Phenylperoxy Radicals

Structure in the Visible Absorption Bands of Jet-Cooled Phenylperoxy Radicals

Hydroxyalkoxy Radicals: Importance of Intramolecular Hydrogen Bonding on Chain Branching Reactions in the Combustion and Atmospheric Decomposition of Hydrocarbons

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

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