Photodissociation of allyl-d2 iodide excited at 193 nm: Stability of highly rotationally excited H2CDCH2 radicals to C–D fission

Szpunar, David E.; Liu, Y.; McCullagh, Martin; Butler, Laurie J.; Shu, Jinian

doi:10.1063/1.1596853

Cited by 21 publications

(23 citation statements)

References 15 publications

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“…Comparison between the trajectory results and two other experiments by Szpunar et al 24,25 is probably not valid, both because the starting conditions are different and because the total excitation energies are different. The trajectories start with zero angular momentum, whereas the allyl radicals in the experiments of are highly rotationally excited.…”

Section: ' Introductionmentioning

confidence: 87%

The Dynamics of Allyl Radical Dissociation

et al. 2011

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Dissociation of the allyl radical, CH(2)CHCH(2), and its deuterated isotopolog, CH(2)CDCH(2), have been investigated using trajectory calculations on an ab initio ground-state potential energy surface calculated for 97,418 geometries at the coupled cluster single and double and perturbative treatment of triple excitations, with the augmented correlation consistent triple-ζ basis set level (CCSD(T)/AVTZ). At an excitation energy of 115 kcal/mol, corresponding to optical excitation at 248 nm, the primary channel is hydrogen loss with a quantum yield of 0.94 to give either allene or propyne in a ratio of 6.4:1. The total dissociation rate for CH(2)CHCH(2) is 6.3 × 10(10) s(-1), corresponding to a 1/e time of 16 ps. Methyl and C(2)H(2) are produced with a quantum yield of 0.06 by three different mechanisms: a 1,3 hydrogen shift followed by C-C cleavage to give methyl and acetylene, a double 1,2 shift followed by C-C cleavage to give methyl and acetylene, or a single 1,2 hydrogen shift followed by C-C cleavage to give methyl and vinylidene. In this last channel, the vinylidene eventually isomerizes to give internally excited acetylene, and the kinetic energy distribution is peaked at much lower energy (6.4 kcal/mol) than that for the other two channels (18 kcal/mol). The trajectory results also predict the v-J correlation, the anisotropy of dissociation, and distributions for the angular momentum of the fragments. The v-J correlation for the CH(3) + HCCH channel is strongest for high rotational levels of acetylene, where v is perpendicular to J. Methyl elimination is anisotropic, with β = 0.66, whereas hydrogen elimination is nearly isotropic. In the hydrogen elimination channel, allene is rotationally excited with a total angular momentum distribution peaked near J = 17. In the methyl elimination channel, the peak of the methyl rotational distribution is at J ≈ 12, whereas the peak of the acetylene rotational distribution is at J ≈ 28.

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Section: ' Introductionmentioning

confidence: 87%

The Dynamics of Allyl Radical Dissociation

et al. 2011

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“…[1][2][3][4] The dissociation and mechanism of isomerization of C 3 H 5 and C 4 H 7 radicals, for example, have been studied both experimentally [5][6][7][8][9][10][11][12] and theoretically [13][14][15][16][17] to understand the branching ratios among various dissociation channels as a function of excitation energy. The reactions of alkenes (C n H 2n ) with atomic chlorine (C ) play important roles in the chemistry of the polar troposphere; [18][19][20] these reactions have also been studied extensively with theory.…”

Section: Introductionmentioning

confidence: 99%

Infrared absorption of trans-1-chloromethylallyl and trans-1-methylallyl radicals produced in photochemical reactions of trans-1,3-butadiene and Cℓ2 in solid para-hydrogen

Bahou

Tanaka

et al. 2012

The Journal of Chemical Physics

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The reactions of chlorine and hydrogen atoms with trans-1,3-butadiene in solid para-hydrogen (p-H(2)) were investigated with infrared (IR) absorption spectra. When a p-H(2) matrix containing Cl(2) and trans-1,3-butadiene was irradiated with ultraviolet light at 365 nm, intense lines at 650.3, 809.0, 962.2, 1240.6 cm(-1), and several weaker ones due to the trans-1-chloromethylallyl radical, ●(CH(2)CHCH)CH(2)Cl, appeared. Observed wavenumbers and relative intensities agree with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++g(2d, 2p) method. That the Cl atom adds primarily to the terminal carbon atom of trans-1,3-butadiene is in agreement with the path of minimum energy predicted theoretically, but in contrast to the reaction of Cl + propene in solid p-H(2) [J. Amicangelo and Y.-P. Lee, J. Phys. Chem. Lett. 1, 2956 (2010)] in which the addition of Cl to the central C atom is favored, likely through steric effects in a p-H(2) matrix. A second set of lines, intense at 781.6, 957.9, 1433.6, 2968.8, 3023.5, 3107.3 cm(-1), were observed when the UV-irradiated Cl(2)/trans-1,3-butadiene/p-H(2) matrix was further irradiated with IR light from a SiC source. These lines are assigned to the trans-1-methylallyl radical, ●(CH(2)CHCH)CH(3), produced from reaction of 1,3-butadiene with a H atom resulted from the reaction of Cl atoms with solid p-H(2) exposed to IR radiation.

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“…l-butler@uchicago.edu to undergo various isomerizations and dissociations. [1][2][3][4][5][6][7] The dissociation dynamics of the unstable radicals are detected by measuring the velocity distribution of the resulting products. The unimolecular dissociation rate of the radical intermediates, as well as the product branching, may be influenced by the partitioning of its internal energy between vibrational and rotational energy.…”

Section: Introductionmentioning

confidence: 99%

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

Brynteson

Butler

2015

The Journal of Chemical Physics

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We present a model which accurately predicts the net speed distributions of products resulting from the unimolecular decomposition of rotationally excited radicals. The radicals are produced photolytically from a halogenated precursor under collision-free conditions so they are not in a thermal distribution of rotational states. The accuracy relies on the radical dissociating with negligible energetic barrier beyond the endoergicity. We test the model predictions using previous velocity map imaging and crossed laser-molecular beam scattering experiments that photolytically generated rotationally excited CD2CD2OH and C3H6OH radicals from brominated precursors; some of those radicals then undergo further dissociation to CD2CD2 + OH and C3H6 + OH, respectively. We model the rotational trajectories of these radicals, with high vibrational and rotational energy, first near their equilibrium geometry, and then by projecting each point during the rotation to the transition state (continuing the rotational dynamics at that geometry). This allows us to accurately predict the recoil velocity imparted in the subsequent dissociation of the radical by calculating the tangential velocities of the CD2CD2/C3H6 and OH fragments at the transition state. The model also gives a prediction for the distribution of angles between the dissociation fragments' velocity vectors and the initial radical's velocity vector. These results are used to generate fits to the previously measured time-of-flight distributions of the dissociation fragments; the fits are excellent. The results demonstrate the importance of considering the precession of the angular velocity vector for a rotating radical. We also show that if the initial angular momentum of the rotating radical lies nearly parallel to a principal axis, the very narrow range of tangential velocities predicted by this model must be convoluted with a J = 0 recoil velocity distribution to achieve a good result. The model relies on measuring the kinetic energy release when the halogenated precursor is photodissociated via a repulsive excited state but does not include any adjustable parameters. Even when different conformers of the photolytic precursor are populated, weighting the prediction by a thermal conformer population gives an accurate prediction for the relative velocity vectors of the fragments from the highly rotationally excited radical intermediates.

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Photodissociation of allyl-d2 iodide excited at 193 nm: Stability of highly rotationally excited H2CDCH2 radicals to C–D fission

Cited by 21 publications

References 15 publications

The Dynamics of Allyl Radical Dissociation

The Dynamics of Allyl Radical Dissociation

Infrared absorption of trans-1-chloromethylallyl and trans-1-methylallyl radicals produced in photochemical reactions of trans-1,3-butadiene and Cℓ2 in solid para-hydrogen

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

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