Structure in the Visible Absorption Bands of Jet-Cooled Phenylperoxy Radicals

Abstract

The visible absorption bands of the phenylperoxy radical in the gas phase have been investigated using cavity ring-down spectroscopy. Jet-cooling was used to reduce the spectral congestion. Structured spectra spanning the range from 17 500 to 19 000 cm–1 are reported for the first time. Analyses of these data have been guided by the results from time-dependent density functional calculations. The observed spectrum was found to be dominated by the bands of the B̃2A″–X̃2A″ transition. An analysis of the rotational contour for the origin band yielded a homogeneous line width of 2.2 cm–1, corresponding to a decay rate of 4.1 × 1011 s–1. The results provide a rationale for the lack of structure in room temperature spectra that have been previously attributed to phenylperoxy. They also indicate that the lower energy region of the spectrum may show resolvable structure at room temperature. If so, this would provide a more definitive signature for monitoring phenylperoxy in kinetic measurements.

Direct Observation of Photodissociation Products from Phenylperoxyl Radicals Isolated in the Gas Phase

“…This estimate is 45 nm blue-shifted from the experimental value of Yu and Lin but not as far as the 337 nm computed by Krauss and Osman . Freel et al also employed TDDFT and found the B3LYP functional with the aug-cc-pVTZ basis performed well when benchmarked to their experimental origin band energy . Using this method, they reported a vertical B̃ ← X̃ transition of 441 nm, in good agreement with our calculations.…”

“…Observations of sharp, characteristic features in the near-IR provided the first unequivocal evidence for an arylperoxyl radical in the gas phase and showed that the location of the à ← X̃ origin transition (i.e., C 6 H 5 OO • T 00 = 1334 nm, 0.93 eV) is not significantly perturbed by the presence of the aryl moiety. In contrast, computational predictions of the energy of the B̃ state of the phenylperoxyl radical predict a significant red-shift compared with alkylperoxyl radicals with estimates of λ max ranging from 337 to 503 nm. ,,, Indeed two groups have reported monitoring a putative B̃ ← X̃ transition near 500 nm at room temperature to establish second order rate constants for the addition of dioxygen to the phenyl radical but in neither instance was a major absorption feature clearly resolved. , More recently, Freel et al reported resolved vibronic bands attributed to the jet-cooled phenylperoxyl radical . The B̃ ← X̃ band origin was assigned at 570.84 nm ( T 00 = 2.17 eV) and vibronic assignments were made to a number of features out to ca.…”

Further studies into the photodissociation pathways of phenylperoxyl radicals

“…0.06). [8] A. M. Mebel and M. C. Lin calculated the isomers of the phenylperoxyl radical at the UHF/6-31G* level. [9] There are several other decomposition pathways at higher energies, including those that lead to the formation of the phenoxy radical (C 6 H 5 O).…”

“…CASSCF a 1.412 1.294 1.422 1.432 1.401 1.384 1.431 1.428 115.6This work. b Calculated at B3LYP/aug-cc-pVTZ level taken from ref[8].Calculated at B3LYP/6-311+G(d) taken from ref[7].…”

Application of phenolic radicals for antioxidants, as active materials in batteries, magnetic materials and ligands for metal-complexes

“…simple radicals can decompose to phenoxyl-radicals or cyclopentadienyl-radicals (Scheme 5). 55,56 Peroxyl-radicals are important in combustion-processes, oxidation of volatile organic compounds in the atmosphere and also play a role in cellular lipid oxidation and DNA damage. 57 The study of phenylperoxyl-radicals is largely focused on their generation, 55 subsequent reactions 57 and decay of these radicals.…”