Partial photoionization cross section and resonance structure of Br

Lin, Dong; Saha, H. P.

doi:10.1103/physreva.59.3614

Cited by 8 publications

(7 citation statements)

References 12 publications

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“…Finally, the ratio is corrected by the ratio of partial photoionization cross sections, which we approximate as 40.0 Mb for HBr + /HBr and DBr + /DBr, 55 and 50.4 Mb for Br + /Br. 52 (In our prior study, 29 The combination of these two ratios yields a total primary photodissociation branching ratio for Br:HBr:DBr as 0.99:0.0064:0.0046. The cofragments formed in the DBr and HBr elimination channels are respectively ethenol, CD 2 CDOH (mass = 47) and the CD 2 CD 2 O (mass = 48) biradical, which may isomerize to acetaldehyde.…”

Section: Resultsmentioning

confidence: 95%

“…This ratio of signal intensities is corrected by a ratio of expected signal, which takes into account 3-D kinematic scattering factors, Jacobian factors, and transit times through the ionizer. Finally, the ratio is corrected by the ratio of partial photoionization cross sections, which we approximate as 40.0 Mb for HBr + /HBr and DBr + /DBr, and 50.4 Mb for Br + /Br . (In our prior study, we erroneously derived σ Br+/Br as 45.4 Mb in footnote 31, and obtained a branching between the C–Br fission channel and the HBr elimination channel as 55.4:1.…”

Section: Resultsmentioning

confidence: 99%

“…The m/e = 79 data was taken at an ionization energy of 15.34 eV, chosen so that the photoionization cross sections of Br( 2 P 1/2 ) and Br( 2 P 3/2 ) would be equal when corrected for their statistical ratios. 52 In ref 33 it is shown that the spin−orbit selected velocity distributions are similar in this system. Figure 4 shows m/e = 79 data collected at additional source angles of 10°, 20°, 30°, and 40°.…”

Section: Resultsmentioning

confidence: 99%

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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: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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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 error bars for the photoionization cross section for ethene at 11.27 eV are small, while the error bars for the vinyl cross section at 11.27 eV are roughly ±20%. While the error in formaldehyde’s absolute cross section is roughly 20%, the photoionization cross section at 11.27 eV was determined from a ratio of signal in an experiment where vinyl and formaldehyde were formed in a 1:1 ratio. Thus the ratio between the formaldehyde photoionization cross section and the vinyl photoionization cross section at 11.27 eV is more precise, ±12%.…”

Section: Resultsmentioning

confidence: 99%

Product Branching from the CH₂CH₂OH Radical Intermediate of the OH + Ethene Reaction

et al. 2011

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Using a crossed laser-molecular beam scattering apparatus and tunable photoionization detection, these experiments determine the branching to the product channels accessible from the 2-hydroxyethyl radical, the first radical intermediate in the addition reaction of OH with ethene. Photodissociation of 2-bromoethanol at 193 nm forms 2-hydroxyethyl radicals with a range of vibrational energies, which was characterized in our first study of this system ( J. Phys. Chem. A 2010 , 114 , 4934 ). In this second study, we measure the relative signal intensities of ethene (at m/e = 28), vinyl (at m/e = 27), ethenol (at m/e = 44), formaldehyde (at m/e = 30), and acetaldehyde (at m/e = 44) products and correct for the photoionization cross sections and kinematic factors to determine a 0.765:0.145:0.026:0.063:<0.01 branching to the OH + C(2)H(4), H(2)O + C(2)H(3), CH(2)CHOH + H, H(2)CO + CH(3), and CH(3)CHO + H product asymptotes. The detection of the H(2)O + vinyl product channel is surprising when starting from the CH(2)CH(2)OH radical adduct; prior studies had assumed that the H(2)O + vinyl products were solely from the direct abstraction channel in the bimolecular collision of OH and ethene. We suggest that these products may result from a frustrated dissociation of the CH(2)CH(2)OH radical to OH + ethene in which the C-O bond begins to stretch, but the leaving OH moiety abstracts an H atom to form H(2)O + vinyl. We compare our experimental branching ratio to that predicted from statistical microcanonical rate constants averaged over the vibrational energy distribution of our CH(2)CH(2)OH radicals. The comparison suggests that a statistical prediction using 1-D Eckart tunneling underestimates the rate constants for the branching to the product channels of OH + ethene, and that the mechanism for the branching to the H(2)O + vinyl channel is not adequately treated in such theories.

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“…25% of the total methyl ion signal is recorded at 12.3 eV photon energy. In the absence of experimental absolute photoionization cross sections, the Br • photoionization cross section at this photon energy is estimated to be 50−100 Mb, based on the calculations of Lin and Saha, 45 the experimental results of Benzaid et al, 46 and the Kr cross section of 45 Mb at similar excess energies above the ionization energy. 47 Because of the higher ionization energy of Br • , almost all of the bromine photoelectrons may be detected.…”

Section: Acs Catalysismentioning

confidence: 98%

Selective Methane Functionalization via Oxyhalogenation over Supported Noble Metal Nanoparticles

et al. 2019

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This article investigates SiO2-supported Ru-, Pt-, Ir-, Rh-, and Pd-based catalysts (1 wt % metal loading) as new catalytic systems for the oxychlorination and oxybromination of methane, both pivotal steps in the halogen-mediated production of commodities from natural gas. Furthermore, this article provides insights into the structure–performance relationships and mechanism of these reactions as a function of the metal and the hydrogen halide. In-depth characterization of the equilibrated catalysts by X-ray diffraction, electron microscopy, Raman, and X-ray photoelectron spectroscopies demonstrate a fast restructuring of the starting oxide nanoparticles into metallic, metal silicide, or metal halide phases. The oxychlorination activity, which decreases in the order: Ru/SiO2 > Pt/SiO2 > Ir/SiO2 > Rh/SiO2 ≈ Pd/SiO2, is enhanced in the presence of metal oxides, while the activity order in oxybromination: Ru/SiO2 ≈ Ir/SiO2 ≈ Pd/SiO2 > Pt/SiO2 > Rh/SiO2 is less dependent on the phase composition. The highest selectivity to chloromethanes (78–83%) and bromomethanes (92–98.5%) at moderate methane conversion (20%), rivaling the performance of the best oxyhalogenation catalysts, is attained over Ir/SiO2, Rh/SiO2, and Pd/SiO2, and correlates with their ability to reduce and form metal halides. Catalyst propensity toward halogenation depends on the halide type, although it is less pronounced at higher loadings (up to 5 wt %), while supporting over other inert carriers has a marginal impact on the restructuring patterns. Finally, kinetic analysis coupled with detection of radical intermediates by operando photoelectron photoion coincidence spectroscopy indicates a significant role of gas-phase halogenation in methane activation via oxyhalogenation. In oxychlorination, the latter pathway has a similar contribution as surface activation for Pd/SiO2, Rh/SiO2, and Pt/SiO2, and major contribution for Ir/SiO2 and Ru/SiO2 catalysts, while in oxybromination, it dominates for all the systems, limiting the potential to enhance the selectivity to mono- over dihalomethanes.

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Partial photoionization cross section and resonance structure of Br

Cited by 8 publications

References 12 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

Product Branching from the CH₂CH₂OH Radical Intermediate of the OH + Ethene Reaction

Selective Methane Functionalization via Oxyhalogenation over Supported Noble Metal Nanoparticles

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Partial photoionization cross section and resonance structure of Br

Cited by 8 publications

References 12 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

Product Branching from the CH2CH2OH Radical Intermediate of the OH + Ethene Reaction

Selective Methane Functionalization via Oxyhalogenation over Supported Noble Metal Nanoparticles

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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

Product Branching from the CH₂CH₂OH Radical Intermediate of the OH + Ethene Reaction