Anomalous polarization: evidence for vibronic coupling in the allyl radical

Getty, James D.; Liu, Xianming; Kelly, Peter B.

doi:10.1016/0009-2614(93)85062-s

Cited by 16 publications

(15 citation statements)

References 14 publications

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“…6 The UV band system starting at 250 nm was studied in detail by absorption spectroscopy, 7 multiphoton ionization, [8][9][10][11][12] and resonance Raman spectroscopy. 4,13,14 Excited state geometries were derived from partially rotationally resolved MPI spectra. 11,12 Although a high oscillator strength of 0.23-0.26 was calculated in a theoretical study for one of the electronic transitions, 15 and also measured in absorption, 16 the complete absence of fluorescence was reported, 4 indicating short lifetimes.…”

Section: Introductionmentioning

confidence: 99%

“…Irradiation at 254 nm, 18 yielded a mixture of allene, propyne, acetylene, methane, and traces of propene, while irradiation at 400 nm supposedly yielded cyclopropyl radicals. 17 Theoretical studies 19 suggested a disrotatory photocyclization upon excitation in the UV bands, a reaction pathway that was supported by the results of a resonance Raman experiment 4,13,14 performed at 224.63 nm, but no direct information on the decay properties of the UV band system is yet available. Thus the results have to be regarded as inconclusive.…”

Section: Introductionmentioning

confidence: 99%

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Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

Schultz¹,

Fischer²

1998

The Journal of Chemical Physics

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Articles you may be interested in Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy J. Chem. Phys. 136, 044302 (2012) We report ͓1ϩ1Ј͔ picosecond time-resolved pump-probe photoelectron spectra of the UV bands of the allyl radical. The experiments are performed in a molecular beam of allyl radicals, generated by supersonic jet flash pyrolysis. Photoelectron spectroscopy in a magnetic bottle is shown to be a suitable method for investigating the photophysics of organic radicals. Lifetimes were obtained for all vibronic bands between 250 and 238 nm previously assigned by MPI spectroscopy to the electronically excited B 2 A 1 , C 2 B 1 , and D 2 B 2 states, with values ranging from 20 ps to 9 ps. The nonradiative decay is due to internal conversion to the electronic ground state. Information on the structure of the allyl cation is deduced from the photoelectron spectrum.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

Schultz¹,

Fischer²

1998

The Journal of Chemical Physics

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“…The allyl radical has been studied using many experimental approaches. Along with the EPR studies, , there have been studies of the UV/vis absorption spectrum, − the IR spectrum in a matrix − and in the gas phase, and the Raman spectrum. − A vibrational force field analysis for the radical and the deuterated isotopomer, 1D , has been provided by Liu et al . Additional spectroscopic information has come from multiphoton ionization studies. − The geometry of allyl radical was originally determined using electron diffraction, but recently a more accurate experimental geometry has been obtained from the measured rotational constants for the C 2 v molecule .…”

Section: Introductionmentioning

confidence: 99%

Photoelectron Spectroscopy of the Allyl and 2-Methylallyl Anions

1996

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The electron affinities of allyl, allyl-d 5 , 2-methylallyl, and 2-methylallyl-d 7 radicals have been determined from the 351 nm photoelectron spectra of the allylic anions. The ions were prepared in a cooled helium flow reactor by the reaction of O -with the corresponding propene. The electron affinities found for the radicals listed above are 0.481 ( 0.008, 0.464 ( 0.006, 0.505 ( 0.006, and 0.493 ( 0.008 eV, respectively. Extensive vibrational structure is observed in all the spectra, as the CCC bending and symmetric stretching modes are activated upon photodetachment. Vibrational frequencies for these modes are obtained for all of the radicals. A second harmonic of an asymmetric CH 2 rocking mode is observed in the spectra of the allyl, allyl-d 5 , and 2-methylallyl anions. Hot bands are used to determine the CCC bending frequencies in the allylic anions. Photoelectron angular distributions were measured for the allyl and 2-methylallyl anions. The photoelectron spectrum of allyl anion is calculated using a modeling procedure that utilizes the vibrational frequencies and geometries from ab initio calculations. This spectrum agrees very well with that obtained experimentally. The measured electron affinities are used together with the previously reported gas-phase acidities of propene and 2-methylpropene to determine the 298 K allylic C-H bond enthalpies for these hydrocarbons, with DH 298 (CH 2 CHCH 2 -H) ) 88.8 ( 0.4 kcal/mol and DH 298 (CH 2 C(CH 3 )CH 2 -H) ) 88.3 ( 2.3 kcal/mol. Methyl substitution at the 2-position of allyl radical is found to have little effect on any of the properties determined in this study.

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“…Placzek's polarizability rule (0 < ρ < 3/4) can be used to determine whether a particular observed frequency is classified as a totally or nontotally symmetric normal mode. , The depolarization ratio (ρ) is defined as the ratio of the Raman scatter perpendicular to the incident radiation ( I ⊥ ) to that of the Raman scatter parallel to the incident radiation ( I ∥ ). For totally symmetric modes, the depolarization ratio is between 0 and 3/4.…”

Section: Discussionmentioning

confidence: 99%

“…Depolarization ratio measurements were measured with a probe polarizer and Raman analyzer . The device incorporates a stacked quartz plate polarizer with 10 quartz slides at Brewster's angle.…”

Section: Methodsmentioning

confidence: 99%

Resonance Raman Spectroscopy of the 1-Methylallyl Radical

et al. 1996

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The first vibrational spectrum of the 1-methylallyl radical is detected using resonance Raman spectroscopy with excitation from 237 to 232 nm. The vibrational frequencies of five symmetric fundamentals, the H 3 C-CCC bend, the CCC bend, the H 3 C-C stretch, the C-H in plane bend, and the CH 2 scissors, of the 1-methylallyl radical are reported. The even overtones of the CH 3 torsion, the C-H out of plane bend, the H 3 C-CCC bend, and the CCC bend are identified. The vibrational assignments of the resonance Raman spectra are based upon comparison with calculated vibrational frequencies generated by UHF method using a 6-31G* basis set and experimental values for the allyl radical, the β-methylallyl radical, and similar molecules. Excitation at 236.05 and 234.95 nm yields significant resonance enhancement of overtone and combination bands associated with the H 3 C-CCC bend and CCC bend, respectively. The variation of intensities in the Raman spectra with excitation wavelength yields excited state vibrational frequencies for the H 3 C-CCC bend and CCC symmetric bend of 305 and 502 cm -1 , respectively. Examination of the observed intensity patterns in the resonance Raman spectra indicates that the initial excited state dynamics of the 1-methylallyl radical are dominated by bending motions of the carbon chain.

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Anomalous polarization: evidence for vibronic coupling in the allyl radical

Cited by 16 publications

References 14 publications

Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

Time-resolved photoelectron spectroscopy of the allyl radical: The lifetimes of the ultraviolet bands

Photoelectron Spectroscopy of the Allyl and 2-Methylallyl Anions

Resonance Raman Spectroscopy of the 1-Methylallyl Radical

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