Benzyl Radical Photodissociation Dynamics at 248 nm

Shapero, Mark; Cole-Filipiak, Neil C.; Haibach-Morris, Courtney; Neumark, Daniel M.

doi:10.1021/acs.jpca.5b07125

Cited by 23 publications

(25 citation statements)

References 63 publications

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“…For comparison values around 20% were observed for the statistical dissociation of allyl 55,56 and propargyl 57 radicals after UV excitation. Again we should also turn to benzyl for comparison: H-atom Rydberg time-of flight spectroscopy of benzyl, photoexcited between 228 and 270 nm into the D-band, yielded f T ≈ 0.29, 17 while translational energy spectroscopy at 248 nm yielded f T ≈ 0.2, 16 i.e., comparable values to the ones observed here at 250 nm. No data are yet available for photodissociation of benzyl from the D 3 state at 305 nm.…”

Section: Discussionsupporting

confidence: 62%

“…Several studies aimed at the kinetics of benzyl to determine rate constants at high-temperature, [8][9][10][11][12][13] and to identify the decomposition products in a high-temperature reactor similar to the one employed in the present work. 14,15 The unimolecular dissociation after excitation at 248 nm was investigated by translational energy spectroscopy 16 and between 228 and 270 nm by Rydberg time-of-flight spectroscopy. 17 H-atom loss leading to fulvenallene has been found to be the dominant reaction pathway in agreement with theory.…”

Section: Introductionmentioning

confidence: 99%

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Photodissociation dynamics of the ortho- and para-xylyl radicals

Pachner

Steglich

Hemberger

et al. 2017

The Journal of Chemical Physics

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The photodissociation dynamics of the CH isomers ortho- and para-xylyl are investigated in a free jet. The xylyl radicals are generated by flash pyrolysis from 2-(2-methylphenyl)- and 2-(4-methylphenyl) ethyl nitrite and are excited into the D state. REMPI- spectra show vibronic structure and the origin of the transition is identified at 32 291 cm for the para- and at 32 132 cm for the ortho-isomer. Photofragment H-atom action spectra show bands at the same energy and thus confirm H-atom loss from xylyl radicals. To gain further insight into the photodissociation dynamics, velocity map images of the hydrogen atom photofragments are recorded. Their angular distribution is isotropic and the translational energy release is in agreement with a dissociation to products in their electronic ground state. Photodissociation of para-xylyl leads to the formation of para-xylylene (CH), while the data for ortho-xylyl agree much better with the isomer benzocyclobutene as the dominant molecular fragment rather than ortho-xylylene. In computations we identified a new pathway for the reaction ortho-xylyl → benzocyclobutene + H with a barrier of 3.39 eV (27 340 cm), which becomes accessible at the employed excitation energy. It proceeds via a combination of scissoring and rotational motion of the -CH and -CH groups. However, the observed rate constants measured by delaying the excitation and ionization laser with respect to each other are significantly faster than computed ones, indicating intrinsic non-RRKM behaviour. A comparably high value of around 30% of the excess energy is released as translation of the H-atom photofragment.

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Section: Discussionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Photodissociation dynamics of the ortho- and para-xylyl radicals

Pachner

Steglich

Hemberger

et al. 2017

The Journal of Chemical Physics

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“…For example, PTS studies of photodissociation of benzyl (C6H5CH2) radicals following excitation in the range 228    270 nm and at  = 248 nm identify C-H bond fission as the dominant decay path (with fulvenallene as the predominant co-fragment), with a minor contribution from the rival CH3 + benzyne product channel. 271,272 Ion imaging studies of the H atoms formed by photolysis of o-and p-xylyl radicals at wavelengths  ~310 nm and ~250 nm are similarly consistent with C-H bond fission after IC to the ground state PES. 273 These data all serve to illustrate the extent of isomerisation (ring opening and H atom transfer) that is required after accessing the ground state PES in order to sample the lowest energy fragmentation pathways.…”

Section: Phenyl Benzyl and Larger Aromatic Radicalsmentioning

confidence: 64%

Photoinduced C–H bond fission in prototypical organic molecules and radicals

Ashfold

Ingle

Karsili

et al. 2019

Phys. Chem. Chem. Phys.

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“…[5][6][7] The pyrolysis of toluene was studied 5 in a quartz flow tube reactor at pressures of 8-15 Torr and temperatures of 1136-1507 K. A more recent study 6 of toluene pyrolysis used a heated alumina (Al 2 O 3 ) micro-reactor coupled to a VUV PIMS driven by tunable radiation from a synchrotron. The 248 nm photochemistry of benzyl radical has been studied 59 by photofragment translational spectroscopy. Dissociation occurs following relaxation from the excited state 60 to the ground state, C 6 H 5 CH 2 ,X 2 B 1 , producing benzyl radicals (C 6 H 5 CH 2 ) * excited by 5 eV.…”

Section: Discussionmentioning

confidence: 99%

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

Buckingham

Porterfield

Kostko

et al. 2016

The Journal of Chemical Physics

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Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 (13)CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 (13)CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).

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Benzyl Radical Photodissociation Dynamics at 248 nm

Cited by 23 publications

References 63 publications

Photodissociation dynamics of the ortho- and para-xylyl radicals

Photodissociation dynamics of the ortho- and para-xylyl radicals

Photoinduced C–H bond fission in prototypical organic molecules and radicals

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

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