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Product branching ratios in photodissociation of phenyl radical: A theoretical ab initio/Rice–Ramsperger–Kassel–Marcus study
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Image of FIG. 1.
FIG. 1.

Potential energy diagram of various dissociation channels of the phenyl radical calculated at the CCSD(T)/CBS//B3LYP/6-311G** + ZPE(B3LYP/6-311G**) level of theory. The numbers show relative energies with respect to c-C6H5 1 computed with two-point and three-point (bold numbers in parentheses) extrapolation to the CBS limit. The numbers in brackets for o-C6H4 + H, i-C4H3 + C2H2, and n-C4H3 + C2H2 give their best available relative energies obtained from the following experimental or theoretical standard enthalpies of formation of individual species at 0 K: ΔH f°(C6H5) = 83.8 kcal/mol (Ref. 50), ΔH f°(i-C4H3) = 119.1 kcal/mol and ΔH f°(n-C4H3) = 131.2 kcal/mol (Refs. 51 and 52), and ΔH f°(C2H2) = 54.5 kcal/mol (Refs. 53 and 54). To evaluate the relative energy of o-C6H4 + H at 0 K, the best available standard enthalpies of formation at 298 K, 80.6, 107.3 ± 3.5, and 52.1 kcal/mol for c-C6H5 (Ref. 50), o-C6H4 (Ref. 55), and H,56 respectively, were used together with thermal corrections to enthalpy from our B3LYP/6-311G** calculations.

Image of FIG. 2.
FIG. 2.

Optimized geometries of the intermediates 1 and 2, conical intersections CI-1, CI-2, and CI-3, the cyclic minimum 1*, and the ring opening transition state TS1-2* in the lowest excited electronic state. Bond lengths are given in angstroms and bond angles in degrees. Bold italic numbers show relative energies of various structures calculated at the CASPT2(9,9)/cc-pVTZ level of theory with respect to 1.


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Table I.

Microcanonical rate constants (s−1) for individual reactions steps calculated at various internal energies.

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Table II.

Calculated product branching ratios (%).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Product branching ratios in photodissociation of phenyl radical: A theoretical ab initio/Rice–Ramsperger–Kassel–Marcus study