Modeling the Rovibrationally Excited C<sub>2</sub>H<sub>4</sub>OH Radicals from the Photodissociation of 2-Bromoethanol at 193 nm

Ratliff, Britni J.; Womack, Caroline C.; Tang, Xin; Landau, Will; Butler, Laurie J.; Szpunar, David E.

doi:10.1021/jp911739a

Cited by 30 publications

(104 citation statements)

References 89 publications

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“…Thus, the radical is generated with high angular momentum and has correspondingly high rotational energy about an axis perpendicular to the plane defined by the centerof-mass of the nascent radical and the impulsive force along the C−Br bond. 32,33 We calculated the moment of inertia about the axis of the CD 2 CD 2 OH radical moiety as 60.7 amu·Å 2 from the Gg conformer (the corresponding value for an impulsive dissociation from the Tt conformer is 64.6 amu·Å 2 ). 33 .…”

Section: Discussionmentioning

confidence: 99%

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate

et al. 2012

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We present the results of our product branching studies of the OH + C 2 D 4 reaction, beginning at the CD 2 CD 2 OH radical intermediate of the reaction, which is generated by the photodissociation of the precursor molecule BrCD 2 CD 2 OH at 193 nm. Using a crossed laser-molecular beam scattering apparatus with tunable photoionization detection, and a velocity map imaging apparatus with VUV photoionization, we detect the products of the major primary photodissociation channel (Br and CD 2 CD 2 OH), and of the secondary dissociation of vibrationally excited CD 2 CD 2 OH radicals (OH, C 2 D 4 / CD 2 O, C 2 D 3 , CD 2 H, and CD 2 CDOH). We also characterize two additional photodissociation channels, which generate HBr + CD 2 CD 2 O and DBr + CD 2 CDOH, and measure the branching ratio between the C−Br bond fission, HBr elimination, and DBr elimination primary photodissociation channels as 0.99:0.0064:0.0046. The velocity distribution of the signal at m/e = 30 upon 10.5 eV photoionization allows us to identify the signal from the vinyl (C 2 D 3 ) product, assigned to a frustrated dissociation toward OH + ethene followed by D-atom abstraction. The relative amount of vinyl and Br atom signal shows the quantum yield of this HDO + C 2 D 3 product channel is reduced by a factor of 0.77 ± 0.33 from that measured for the undeuterated system. However, because the vibrational energy distribution of the deuterated radicals is lower than that of the undeuterated radicals, the observed reduction in the water + vinyl product quantum yield likely reflects the smaller fraction of radicals that dissociate in the deuterated system, not the effect of quantum tunneling. We compare these results to predictions from statistical transition state theory and prior classical trajectory calculations on the OH + ethene potential energy surface that evidenced a roaming channel to produce water + vinyl products and consider how the branching to the water + vinyl channel might be sensitive to the angular momentum of the β-hydroxyethyl radicals.

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Section: Discussionmentioning

confidence: 99%

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate

et al. 2012

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“…The details of this apparatus and the experimental results are described elsewhere. 1,13 In short, a supersonic molecular beam of acetyl chloride molecules was photodissociated at 235 nm, and the Cl and CH 3 CO cofragments were photoionized and detected with velocity map imaging to measure the distributions of velocities, P Cl (υ) and P acetyl (υ) respectively. The acetyl radicals were produced in a range of velocities corresponding to internal energies that span the barrier to further dissociation.…”

Section: Previous Experimental Resultsmentioning

confidence: 99%

“…1 When applied to the highly internally excited CH 2 CH 2 OH radicals formed from the photodissociation of 2-bromoethanol at 193 nm, this model accurately predicted the percentage of radicals that were partitioned enough rotational energy at each relative kinetic energy to remain stable to further dissociation. 1 The excited state of 2-bromoethanol is known to be repulsive in the Franck-Condon region, 11,12 which made an impulsive model a reasonable assumption. In this paper, we test the utility of the model for predicting the partitioning of internal energy between rotation and vibration for the dissociation of a molecule, acetyl chloride, not on a steeply repulsive potential, but on an excited state with a C-halogen bond fission transition state outside the FranckCondon region.…”

Section: Introductionmentioning

confidence: 94%

Assessing an Impulsive Model for Rotational Energy Partitioning to Acetyl Radicals from the Photodissociation of Acetyl Chloride at 235 nm

et al. 2010

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This work uses the photodissociation of acetyl chloride to assess the utility of a recently proposed impulsive model when the dissociation occurs on an excited electronic state that is not repulsive in the Franck-Condon region. The impulsive model explicitly includes an average over the vibrational quantum states of acetyl chloride when it calculates an impact parameter for fission of the C-Cl bond, as well as the distribution of thermal energy in the photolytic precursor. The experimentally determined stability of the resulting acetyl radical to subsequent dissociation is the key observable that allows us to test the model's ability to predict the partitioning of energy between rotation and vibration of the radical. We compare the model's predictions for three different assumed geometries at which the impulsive force might act, generating the relative kinetic energy and the concomitant rotational energy in the acetyl radical. Assuming that the impulsive force acts at the transition state for C-Cl fission on the S 1 excited state gives a poor prediction; the model predicts far more energy in rotation of the acetyl radical than is consistent with the measured velocity map imaging spectrum of the stable radicals. The best prediction results from using a geometry derived from the classical trajectory calculations on the excited state potential energy surface. We discuss the insight gained into the excited state dissociation dynamics of acetyl chloride and, more generally, the utility of using the impulsive model in conjunction with excited state trajectory calculations to predict the partitioning of internal energy between rotation and vibration for radicals produced from the photolysis of halogenated precursors.

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“…The first model is an extension of one used by Ratliff et al 42 and Womack et al, 43 which is used to predict the rotational energy imparted to the nascent radicals from the C−Br photofission. As in the prior work, the model uses the measured recoil kinetic energy distribution and the geometry of the precursor in the Franck−Condon region of the repulsive excited state to estimate the distribution of angular momenta in the nascent radicals.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Consequently, there is less energy available to the vibrational modes of the molecule, resulting in a higher fraction of stable radicals than in the absence of any rotation. To predict the rotational energy imparted to the nascent recoiling C 3 H 6 OH radicals we use a method similar to that used by Ratliff et al 42 and Womack et al, 43 but while their model used the scalar value of inertia, our model includes the full tensor of inertia, as the former is correct only for rotation about a principle axis. 44 This method uses conservation of angular momentum to determine the amount of rotational energy imparted to the recoiling C 3 H 6 OH fragments as a function of the recoil velocity vector along the C−Br bond.…”

Section: ■ Introductionmentioning

confidence: 99%

Radical Intermediates in the Addition of OH to Propene: Photolytic Precursors and Angular Momentum Effects

et al. 2014

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We investigate the photolytic production of two radical intermediates in the reaction of OH with propene, one from addition of the hydroxyl radical to the terminal carbon and the other from addition to the center carbon. In a collision-free environment, we photodissociate a mixture of 1-bromo-2-propanol and 2-bromo-1-propanol at 193 nm to produce these radical intermediates. The data show two primary photolytic processes occur: C−Br photofission and HBr photoelimination. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling bromine atoms, yielding the distribution of kinetic energies of the nascent C 3 H 6 OH radicals + Br. Resolving the velocity distributions of Br( 2 P 1/2 ) and Br( 2 P 3/2 ) separately with 2 + 1 REMPI allows us to determine the total (vibrational + rotational) internal energy distribution in the nascent radicals. Using an impulsive model to estimate the rotational energy imparted to the nascent C 3 H 6 OH radicals, we predict the percentage of radicals having vibrational energy above and below the lowest dissociation barrier, that to OH + propene; it accurately predicts the measured velocity distribution of the stable C 3 H 6 OH radicals. In addition, we use photofragment translational spectroscopy to detect several dissociation products of the unstable C 3 H 6 OH radicals: OH + propene, methyl + acetaldehyde, and ethyl + formaldehyde. We also use the angular momenta of the unstable radicals and the tensor of inertia of each to predict the recoil kinetic energy and angular distributions when they dissociate to OH + propene; the prediction gives an excellent fit to the data. ■ INTRODUCTIONThe oxidation of unsaturated hydrocarbons by the hydroxyl radical is an important reaction in both atmospheric and combustion chemistry. Our experiment focuses on the reaction of OH with propene, a simple unsaturated hydrocarbon with two sites at which addition of the OH may occur. To date, many studies on the reaction rate over a wide range of temperatures have been performed on this system, both experimental 1−31 and theoretical. 32−34 These studies have shown that the addition of OH to propene dominates at temperatures below 500 K. Beyond 500 K, hydrogen abstraction becomes an important part of the mechanism and begins to dominate at much higher temperatures. In addition, ethene and propene flame studies have given evidence for the presence of enols, which has increased interest in the product branching resulting from OH-initiated oxidation. 35,36 The addition of the hydroxyl radical to propene offers a wider variety of products than the addition of OH to ethene as the addition to propene may occur via two pathways: addition to the terminal carbon and addition to the center carbon. Experimental results show the branching between the center and terminal carbon addition favors the terminal carbon, with approximately 65−75% of additions leading to terminal carbon addition. 37−39 Theory has given similar results, yielding predictions of ∼65% of additions to the ...

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Modeling the Rovibrationally Excited C₂H₄OH Radicals from the Photodissociation of 2-Bromoethanol at 193 nm

Cited by 30 publications

References 89 publications

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate

Assessing an Impulsive Model for Rotational Energy Partitioning to Acetyl Radicals from the Photodissociation of Acetyl Chloride at 235 nm

Radical Intermediates in the Addition of OH to Propene: Photolytic Precursors and Angular Momentum Effects

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Modeling the Rovibrationally Excited C2H4OH Radicals from the Photodissociation of 2-Bromoethanol at 193 nm

Cited by 30 publications

References 89 publications

Photoproduct Channels from BrCD2CD2OH at 193 nm and the HDO + Vinyl Products from the CD2CD2OH Radical Intermediate

Photoproduct Channels from BrCD2CD2OH at 193 nm and the HDO + Vinyl Products from the CD2CD2OH Radical Intermediate

Assessing an Impulsive Model for Rotational Energy Partitioning to Acetyl Radicals from the Photodissociation of Acetyl Chloride at 235 nm

Radical Intermediates in the Addition of OH to Propene: Photolytic Precursors and Angular Momentum Effects

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Modeling the Rovibrationally Excited C₂H₄OH Radicals from the Photodissociation of 2-Bromoethanol at 193 nm

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate

Photoproduct Channels from BrCD₂CD₂OH at 193 nm and the HDO + Vinyl Products from the CD₂CD₂OH Radical Intermediate