Site-specific hydrogen-atom elimination in photoexcited ethyl radical

Chicharro, David V.; Poullain, Sonia Marggi; Zanchet, Alexandre; Bouallagui, Aymen; Garcı́a-Vela, A.; Senent, María Luisa; Rubio-Lago, Luis; Bañares, Luis

doi:10.1039/c9sc02140j

Cited by 14 publications

(57 citation statements)

References 38 publications

(39 reference statements)

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“…To keep the homogeneity of the vertical excitations compared to our previous work 22 , the same level of calculation and procedure were repeated. More specifically, state-averaged complete active space self-consistent field (SA-CASSCF) calculations have been performed with an active space consisting of 13 electrons in 10 orbitals, the two first orbitals being kept closed.…”

Section: Theoreticalmentioning

confidence: 99%

“…Due to a convergence problem in the excited states, the Davidson correction was not applied to the MRCI energies. In order to ensure homogeneity in all calculations, including our previous work 22 and in particular to employ the same active orbitals, all ab initio calculations (for both the C s and C 2v geometries) were performed using the C 1 group of symmetry, assuming the additional cost of the calculations and a limitation on the number of electronic states that can be calculated.…”

Section: Theoreticalmentioning

confidence: 99%

“…for the 3s-Rydberg state excitation, the differences between both methods to produce ethyl radicals are now striking. While a blot dominates the image leading to a Boltzman-type distribution when ethyl radicals are produced by pyrolysis, photoexcitation of vibrationally-hot ethyl radicals as formed by in situ photolysis, leads to a pronounced second contribution: an isotropic ring at higher radius, yielding a sharp Gaussian peak in the TED 22 . Besides, the Boltzmann-type distributions differ: in Figure 5(a), the slow component presents a maximum of intensity at threshold energies, while in Figure 5(b), its maximum is around <E T > = 0.5 eV and it is characterized by a larger full width at half maximum (FWHM).…”

Section: Two-color Experiments: Photodissociation From the 3pmentioning

confidence: 99%

“…It can be attributed to the different REMPI schemes employed, the (3+1) REMPI used in Ref. 22 allowing a great energy resolution in spite of a lower intensity.…”

Section: Two-color Experiments: Photodissociation From the 3pmentioning

confidence: 99%

“…We have recently investigated the photodynamics following excitation of the ethyl radical in the 3p Rydberg state by means of a pump-probe scheme and velocity map imaging 22 . A novel mechanism for site-specific H-atom elimination, leading to CH 3 CH + H, was reported and discussed with the aid of ab initio calculations, including potential energy curves and non-adiabatic coupling matrix elements.…”

Section: Introductionmentioning

confidence: 99%

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The 3s versus 3p Rydberg state photodissociation dynamics of the ethyl radical

Poullain

Chicharro

Zanchet

et al. 2019

Phys. Chem. Chem. Phys.

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Section: Theoreticalmentioning

confidence: 99%

Section: Theoreticalmentioning

confidence: 99%

Section: Two-color Experiments: Photodissociation From the 3pmentioning

confidence: 99%

“…It can be attributed to the different REMPI schemes employed, the (3+1) REMPI used in Ref. 22 allowing a great energy resolution in spite of a lower intensity.…”

Section: Two-color Experiments: Photodissociation From the 3pmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The 3s versus 3p Rydberg state photodissociation dynamics of the ethyl radical

Poullain

Chicharro

Zanchet

et al. 2019

Phys. Chem. Chem. Phys.

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DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

Ortega

Zanchet

Sanz-Sanz

et al. 2020

Chemistry A European J

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Despite being a very strong oxidizing agent, most organic molecules are not oxidized in the presence of O2 at room temperature because O2 is a diradical whereas most organic molecules are closed‐shell. Oxidation then requires a change in the spin state of the system, which is forbidden according to non‐relativistic quantum theory. To overcome this limitation, oxygenases usually rely on metal or redox cofactors to catalyze the incorporation of, at least, one oxygen atom into an organic substrate. However, some oxygenases do not require any cofactor, and the detailed mechanism followed by these enzymes remains elusive. To fill this gap, here the mechanism for the enzymatic cofactor‐independent oxidation of 3,5‐dihydroxyphenylacetyl‐CoA (DPA‐CoA) is studied by combining multireference calculations on a model system with QM/MM calculations. Our results reveal that intersystem crossing takes place without requiring the previous protonation of molecular oxygen. The characterization of the electronic states reveals that electron transfer is concomitant with the triplet–singlet transition. The enzyme plays a passive role in promoting the intersystem crossing, although spontaneous reorganization of the water wire connecting the active site with the bulk presets the substrate for subsequent chemical transformations. The results show that the stabilization of the singlet radical‐pair between dioxygen and enolate is enough to promote spin‐forbidden reaction without the need for neither metal cofactors nor basic residues in the active site.

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Photodissociation Dynamics of the Cyclohexyl Radical from the 3p Rydberg State at 248 nm

2021

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The photodissociation of jet-cooled cyclohexyl was studied by exciting the radicals to their 3p Rydberg state using 248 nm laser light and detecting photoproducts by photofragment translational spectroscopy. Both H-atom loss and dissociation to heavy fragment pairs are observed. The H-atom loss channel exhibits a two-component translational energy distribution. The fast photoproduct component is attributed to impulsive cleavage directly from an excited state, likely the Rydberg 3s state, forming cyclohexene. The slow component is due to statistical decomposition of hot cyclohexyl radicals that internally convert to the ground electronic state prior to H-atom loss. The fast and slow components are present in a ~0.7:1 ratio, similar to findings in other alkyl radicals. Internal conversion to the ground state also leads to ring-opening followed by dissociation to 1-buten-4-yl + ethene in comparable yield to H-loss, with the C4H7 fragment containing enough internal energy to dissociate further to butadiene via H-atom loss. A very minor ground-state C5H8 + CH3 channel is observed, attributed predominantly to 1,3pentadiene formation. The ground-state branching ratios agree well with RRKM calculations, which also predict C4H6 + C2H5 and C3H6 + C3H5 channels with similar yield to C5H8 + CH3. If these channels were active it was at levels too low to be observed. I.Previous photodissociation studies from the 3s and 3p Rydberg states of ethyl by Zhang, Fischer, Bañares and co-workers detected H atoms ejected with a bimodal kinetic energy distribution. [14][15][16][17] The 'fast' H atoms result from direct dissociation from the excited electronic state, while the 'slow' population is attributed to statistical dissociation following internal conversion to the ground state. The observation of angular distributions that are anisotropic for the fast H atoms and isotropic for the slow H atoms supports these mechanisms. These fast and slow dissociation channels occur in a roughly 0.4:1 ratio depending on the initial and final states of ethyl used in the experiment. For ethyl excited to the 3s state, the fast dissociation channel has a dissociation time constant of ~300 fs, while for the slow channel it is ~6-7 ps. 18

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Site-specific hydrogen-atom elimination in photoexcited ethyl radical

Abstract: The photochemistry of the ethyl radical following excitation to the 3p Rydberg state is investigated in a joint experimental and theoretical study.

Cited by 14 publications

References 38 publications

The 3s versus 3p Rydberg state photodissociation dynamics of the ethyl radical

The 3s versus 3p Rydberg state photodissociation dynamics of the ethyl radical

DpgC‐Catalyzed Peroxidation of 3,5‐Dihydroxyphenylacetyl‐CoA (DPA‐CoA): Insights into the Spin‐Forbidden Transition and Charge Transfer Mechanisms**

Photodissociation Dynamics of the Cyclohexyl Radical from the 3p Rydberg State at 248 nm

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