ESR investigation of the photoisomerization of OClO to ClOO in an H2SO4 glass: Magnetophotoselection and kinetics

Adrian, Frank J.; Bohandy, J.; Kim, B. F.

doi:10.1063/1.451026

Cited by 45 publications

(32 citation statements)

References 25 publications

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“…Matrix spectra of O C l O also exhibit significant broadening compared to the gas-phase spectrum (23,24,47,48). This broadening most likely results from the heterogeneity of the sites occupied by OClO.…”

Section: Photoreactivity Of Chlorine Dioxidementioning

confidence: 97%

“…Thus, matrices, like solutions, preclude obtaining geometric information about electronically excites states of O C l O from a spectroscopic analysis. Photolysis studies (23,24,47,48) there would be a substantial chanpe in the D quantum efficiency for this process in the matrix as compared to that in the gas phase. Thus, the behavior of O C l O in cold matrices is sienificantlv different from that ob-" served in the gas phase and in room-temperature solution.…”

Section: Photoreactivity Of Chlorine Dioxidementioning

confidence: 98%

“…Although a complete discussion of 0, (23,24) and ultrafast measurements in solution (25)(26)(27)(28)(29). In good agreement with experiment, calculations by Peterson and Werner (21) suggest a geometry in which the C1-0 agd 0-0 bond lengths are 2.139 and 1.291 A, respectively, and the bond angle is 115.7"; the 0-0 bond length is nearly that of free 0, (1.207 A).…”

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confidence: 99%

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The Photoreactivity of Chlorine Dioxide

Vaida

Simon

1995

Science

154

140

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Determining the detailed photoreactivity of radicals that are of importance in atmospheric processes requires information from both laboratory and field measurements and theoretical calculations. Laboratory experiments and quantum calculations have been used to develop a comprehensive understanding of the photoreactivity of chlorine dioxide (OCIO). The photoreactivity is strongly dependent on the medium (gas phase, liquid solution, or cryogenic matrix). These data reveal details of the complex chemistry of OCIO. The potential role of this radical in stratospheric ozone depletion is discussed in accord with these laboratory measurements.

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Section: Photoreactivity Of Chlorine Dioxidementioning

confidence: 97%

Section: Photoreactivity Of Chlorine Dioxidementioning

confidence: 98%

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confidence: 99%

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The Photoreactivity of Chlorine Dioxide

Vaida

Simon

1995

Science

154

140

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“…3). Interference from intermediate radicals such as CIO, CI or CIO 3 was discarded because of their low concentrations in this system [18].…”

Section: Chemicalsmentioning

confidence: 99%

Determination of differential quantum yields in solution by electron paramagnetic resonance spectroscopy

2002

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Quantitative kinetic studies on the photochemistry of paramagnetic species in solution may be carried out by electron paramagnetic resonance (EPR) spectroscopy. A cylindrical cell can be used as photochemical reactor, but the internal diameter should be less than 1.7 mm in order to achieve the resonance of an aqueous sample in an X-band (9-10 GHz ) spectrometer. In this paper we present a detailed analysis of the fractions of incident light that are reflected, transmitted and absorbed by a liquid solution in a quartz cylindrical cell placed in the optical cavity of ah X-band EPR spectrometer. Since the photolysis cell is irradiated perpendicularly to its axis, variable angles of incidente have been considered to calculate the transmission and reflection coefficients from Fresnel equations. Polarization of light has been also taken into account in the evaluation of the coefficients. The procedure proposed here is adequate for the evaluation of the absorbed light in the determination of quantum yields. The continuous photolysis at 366 nm of symmet¡ chlorine dioxide (OC10) in aqueous solution was considered as an example. The initial differential quantum yield obtained for OC10 photodecomposition in aqueous solution was I• ~--0.55___0.04.

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“…In matrix isolation experiments at low temperature, Arkell and Schwager, 46 and others, [47][48][49] reported that photolysis of OClO led to formation of ClOO. Unlike symmetric OClO which can be readily synthesized and studied, the ClOO peroxy isomer remains poorly characterized because of its extreme reactivity due to a very weak Cl-O 2 bond ͑D 0 ϭ4.5 kcal/mol͒.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation dynamics of OClO

Davis

Lee

1996

The Journal of Chemical Physics

112

111

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Photofragment translational energy spectroscopy was used to study the dissociation dynamics of a range of electronically excited OClO(A 2 A 2 ) vibrational states. For all levels studied, corresponding to OClO(A 2 A 2 ←X 2 B 1 ) excitation wavelengths between 350 and 475 nm, the dominant product ͑Ͼ96%͒ was ClO͑ 2 ⌸͒ϩO( 3 P). We also observed production of ClϩO 2 with a quantum yield of up to 3.9Ϯ0.8% near 404 nm, decreasing at longer and shorter wavelengths. The branching ratios between the two channels were dependent on the OClO(A 2 A 2 ) excited state vibrational mode. The ClϩO 2 yield was enhanced slightly by exciting A 2 A 2 levels having symmetric stretchingϩbending, but diminished by as much as a factor of 10 for neighboring peaks associated with symmetric stretchingϩasymmetric stretching. Mode specificity was also observed in the vibrationally state resolved translational energy distributions for the dominant ClO͑ 2 ⌸͒ϩO( 3 P) channel. The photochemical dynamics of OClO possesses two energy regimes with distinctly different dynamics observed for excitation energies above and below ϳ3.1 eV ͑ϳ400 nm͒. At excitation energies below 3.1 eV ͑Ͼ400 nm͒, nearly all energetically accessible ClO vibrational energy levels were populated, and the minor ClϩO 2 channel was observed. Although at least 20% of the O 2 product is formed in the ground (X 3 ⌺ g Ϫ ) state, most O 2 is electronically excited (a 1 ⌬ g ). At EϽ3.1 eV, both dissociation channels occur by an indirect mechanism involving two nearby excited states, 2 A 1 and 2 B 2 . Long dissociation time scales and significant parent bending before dissociation led to nearly isotropic polarization angular distributions ͑␤ϳ0͒. At excitation energies above 3.1 eV ͑Ͻ400 nm͒, the ClϩO 2 yield began to decrease sharply, with this channel becoming negligible at Ͻ370 nm. At these higher excitation energies, the ClO product was formed with relatively little vibrational energy and a large fraction of the excess energy was channeled into ClOϩO translational energy. The photofragment anisotropy parameter ͑␤͒ also increased, implying shorter dissociation time scales. The sharp change in the disposal of excess energy into the ClO products, the decrease of ClϩO 2 production, and more anisotropic product angular distributions at EϾ3.1 eV signify the opening of a new ClOϩO channel. From our experimental results and recent ab initio calculations, dissociation at wavelengths shorter than 380 nm to ClOϩO proceeds via a direct mechanism on the optically prepared A 2 A 2 surface over a large potential energy barrier. From the ClO͑ 2 ⌸͒ϩO( 3 P) translational energy distributions, D 0 ͑O-ClO͒ was found to be less than or equal to 59.0Ϯ0.2 kcal/mol.

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ESR investigation of the photoisomerization of OClO to ClOO in an H2SO4 glass: Magnetophotoselection and kinetics

Cited by 45 publications

References 25 publications

The Photoreactivity of Chlorine Dioxide

The Photoreactivity of Chlorine Dioxide

Determination of differential quantum yields in solution by electron paramagnetic resonance spectroscopy

Photodissociation dynamics of OClO

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