The absorption spectrum and absolute absorption cross sections of acetylperoxy radicals, CH3C(O)O2 in the near IR

Rolletter, Michael; Assaf, Emmanuel; Assali, Mohamed; Fuchs, Hendrik; Fittschen, C.

doi:10.1016/j.jqsrt.2020.106877

Cited by 3 publications

(7 citation statements)

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“…HO 2 profiles are then obtained by subtracting online–offline (red dots in Figure a). The absorption cross sections of this transition have been determined several times, and a cross section of σ HO 2 ,100 Torr = (2.0 ± 0.3) × 10 –19 cm 2 is used in this work. CH 3 C(O)O 2 is quantified in the Ã–X̃ electronic transition at 6497.94 cm –1 (blue dots on right y scale in Figure b) with an absorption cross section of σ CH 3 C(O)O 2 = 3.3 × 10 –20 cm 2 . Even though the transition is less structured than the HO 2 spectrum, absorption–time profiles at different wavelengths always lead to identical shapes: in Figure b is shown again the offline HO 2 signal from Figure a, now scaled on the left y axis to overlay with the CH 3 C(O)O 2 signal.…”

Section: Results and Discussionmentioning

confidence: 97%

“…CH 3 C(O)O 2 is quantified in the Ã–X̃ electronic transition at 6497.94 cm –1 (blue dots on right y scale in Figure b) with an absorption cross section of σ CH 3 C(O)O 2 = 3.3 × 10 –20 cm 2 . Even though the transition is less structured than the HO 2 spectrum, absorption–time profiles at different wavelengths always lead to identical shapes: in Figure b is shown again the offline HO 2 signal from Figure a, now scaled on the left y axis to overlay with the CH 3 C(O)O 2 signal.…”

Section: Results and Discussionmentioning

confidence: 97%

“…• CH 3 C(O)O 2 is quantified in the A ̃−X ̃electronic transition at 6497.94 cm −1 (blue dots on right y scale in Figure 1b) with an absorption cross section of σ CHd 3 C(O)Od 2 = 3.3 × 10 −20 cm 2 . 30 Even though the transition is less structured than the HO 2 spectrum, absorption−time profiles at different wavelengths always lead to identical shapes: in Figure 1b The radicals decay mostly by self-reaction; therefore, the linear regression of a plot of 1/α = f(t) allows a more reliable extrapolation to α t=0 s , the absorption coefficient just after the photolysis pulse. 26 Figure 2 shows a typical example with four different Cl concentrations: graph (a) shows a plot of 1/α 6638,58 cm −1 = f(t) for the experiments with CH 3 OH, and graph (b) shows 1/α 7491.31 cm −1 = f(t) for the same Cl concentration in the presence of CH 3 C(O)CH 3 .…”

Section: ■ Experimental Setupmentioning

confidence: 98%

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Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms

Assali

Fittschen

2022

J. Phys. Chem. A

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The rate constant for the self-reaction of the acetonyl peroxy radicals, CH3C(O)CH2O2, has been determined using laser photolysis/continuous wave cavity ring down spectroscopy (cw-CRDS). CH3C(O)CH2O2 radicals have been generated from the reaction of Cl atoms with CH3C(O)CH3, and the concentration time profiles of four radicals (HO2, CH3O2, CH3C(O)O2, and CH3C(O)CH2O2) have been determined by cw-CRDS in the near-infrared. The rate constant for the self-reaction was found to be k = (5.4 ± 1.4) × 10–12 cm3 s–1, in good agreement with a recently published value (Zuraski, K., et al. J. Phys. Chem. A 2020, 124, 8128); however, the branching ratio for the radical path was found to be ϕ1b = (0.6 ± 0.1), which is well above the recently published value (0.33 ± 0.13). The influence of a fast reaction of Cl atoms with the CH3C(O)CH2O2 radical became evident under some conditions; therefore, this reaction has been investigated in separate experiments. Through the simultaneous fitting of all four radical profiles to a complex mechanism, a very fast rate constant of k = (1.35 ± 0.8) × 10–10 cm3 s–1 was found, and experimental results could be reproduced only if Cl atoms would partially react through H-atom abstraction to form the Criegee intermediate with a branching fraction of ϕCriegee = (0.55 ± 0.1). Modeling the HO2 concentration–time profiles was possible only if a subsequent reaction of the Criegee intermediate with CH3C(O)CH3 was included in the mechanism leading to HO2 formation with a rate constant of k = (4.5 ± 2.0) × 10–14 cm3 s–1.

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Section: Results and Discussionmentioning

confidence: 97%

Section: Results and Discussionmentioning

confidence: 97%

Section: ■ Experimental Setupmentioning

confidence: 98%

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Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms

Assali

Fittschen

2022

J. Phys. Chem. A

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“…A peak absorption cross section of 1.0 × 10 −20 cm 2 at 5582.5 cm −1 was measured for the origin band, and its value is given in Table 2. A subsequent investigation of CH 3 C(O)O 2 by Rolletter et al 10 has determined the peak cross section for the O−O stretch band at 6510.7 cm −1 to be 0.49 × 10 −20 cm 2 . Since the relative intensities of these two bands differ by about a factor of 2 in the observed spectra, the cross section values are quite consistent.…”

Section: Ethyl Peroxymentioning

confidence: 99%

Calculated and Empirical Values of Vibronic Transition Dipole Moments of Reactive Chemical Intermediates for Determination of Concentrations

et al. 2023

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Absorption spectroscopy has long been known as a technique for making molecular concentration measurements and has received enhanced visibility in recent years with the advent of new techniques, like cavity ring-down spectroscopy, that have increased its sensitivity. To apply the method, it is necessary to have a known molecular absorption cross section for the species of interest, which typically is obtained by measurements of a standard sample of known concentration. However, this method fails if the species is highly reactive, and indirect means for attaining the cross section must be employed. The HO2 and alkyl peroxy radicals are examples of reactive species for which absorption cross sections have been reported. This work explores and describes for these peroxy radicals the details of an alternative approach for obtaining these cross sections using quantum chemistry methods for the calculation of the transition dipole moment upon whose square the cross section depends. Likewise, details are given for obtaining the transition moment from the experimentally measured cross sections of individual rovibronic lines in the near-IR Ã–X̃ electronic spectrum of HO2 and the peaks of the rotational contours in the corresponding electronic transitions for the alkyl (methyl, ethyl, and acetyl) peroxy radicals. In the case of the alkyl peroxy radicals, good agreement for the transition moments, ≈20%, is found between the two methods. However, rather surprisingly, the agreement is significantly poorer, ≈40%, for the HO2 radical. Possible reasons for this disagreement are discussed.

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“…The relative spectrum has already been measured by Zalyubovsky et al [41] in a large wavelength range and the absolute absorption cross section of the strongest band at 5582 cm −1 has been estimated. In a recent work, our group has determined absolute absorption cross sections in two wavelength ranges from 6094 to 6180 cm −1 and from 6420 to 6600 cm −1 , corresponding to the C(O)O bend and to the OO stretch transition, respectively [42], whereby the cross sections were determined relative to the absorption cross section of HO 2…”

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confidence: 99%

Rate Constants and Branching Ratios for the Self-Reaction of Acetyl Peroxy (CH3C(O)O2•) and Its Reaction with CH3O2

Assali

Fittschen

2022

Atmosphere

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The self-reaction of acetylperoxy radicals (CH3C(O)O2•) (R1) as well as their reaction with methyl peroxy radicals (CH3O2•) (R2) have been studied using laser photolysis coupled to a selective time resolved detection of three different radicals by cw-CRDS in the near-infrared range: CH3C(O)O2• was detected in the Ã-X˜ electronic transition at 6497.94 cm−1, HO2• was detected in the 2ν1 vibrational overtone at 6638.2 cm−1, and CH3O2• radicals were detected in the Ã-X˜ electronic transition at 7489.16 cm−1. Pulsed photolysis of different precursors at different wavelengths, always in the presence of O2, was used to generate CH3C(O)O2• and CH3O2• radicals: acetaldehyde (CH3CHO/Cl2 mixture or biacetyle (CH3C(O)C(O)CH3) at 351 nm, and acetone (CH3C(O)CH3) or CH3C(O)C(O)CH3 at 248 nm. From photolysis experiments using CH3C(O)C(O)CH3 or CH3C(O)CH3 as precursor, the rate constant for the self-reaction was found with k1 = (1.3 ± 0.3) × 10−11 cm3s−1, in good agreement with current recommendations, while the rate constant for the cross reaction with CH3O2• was found to be k2 = (2.0 ± 0.4) × 10−11 cm3s−1, which is nearly two times faster than current recommendations. The branching ratio of (R2) towards the radical products was found at 0.67, compared with 0.9 for the currently recommended value. Using the reaction of Cl•-atoms with CH3CHO as precursor resulted in radical profiles that were not reproducible by the model: secondary chemistry possibly involving Cl• or Cl2 might occur, but could not be identified.

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The absorption spectrum and absolute absorption cross sections of acetylperoxy radicals, CH3C(O)O2 in the near IR

Cited by 3 publications

References 37 publications

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms

Calculated and Empirical Values of Vibronic Transition Dipole Moments of Reactive Chemical Intermediates for Determination of Concentrations

Rate Constants and Branching Ratios for the Self-Reaction of Acetyl Peroxy (CH3C(O)O2•) and Its Reaction with CH3O2

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