scholarly journals OH production from the photolysis of isoprene-derived peroxy radicals: cross-sections, quantum yields and atmospheric implications

2017 ◽  
Vol 19 (3) ◽  
pp. 2332-2345 ◽  
Author(s):  
Robert F. Hansen ◽  
Tom R. Lewis ◽  
Lee Graham ◽  
Lisa K. Whalley ◽  
Paul W. Seakins ◽  
...  
Keyword(s):  
Cross Sections ◽  
Quantum Yields ◽  
Oh Radical ◽  
Peroxy Radicals ◽  
Near Ultraviolet ◽  
Radical Production ◽  
Ultraviolet Photolysis

The OH radical production from the near-ultraviolet photolysis of peroxy radicals derived from isoprene has been investigated.

Wavelength controlled production of SO4- radicals in the ultraviolet photolysis of ceric sulfate solutions

1984 ◽  
Vol 37 (3) ◽  
pp. 475 ◽  
Author(s):  
RW Matthews
Keyword(s):  
Rate Constants ◽  
Photochemical Reaction ◽  
Transfer Reaction ◽  
Quantum Yields ◽  
Oh Radical ◽  
Transfer Energy ◽  
Fluorescence Measurements ◽  
Sulfate Solutions ◽  
Ultraviolet Photolysis ◽  
Primary Photochemical Reaction

Solutions of cerium(III)/(IV) and formic acid in 0.4 M sulfuric acid have been photolysed under 254 nm and 365 nm light. Marked differences in the reaction kinetics and quantum yields are observed at the two different wavelengths. At 365 nm, the reactions leading to cerium(IV) reduction are caused almost exclusively by the SO4- radical. The ratio of rate constants, k(SO4- + CeIII)/ k(SO4- + HCOOH), is 116 � 11 and the quantum yield of sulfate radicals, ф(SO4-), is 0.023 � 0.002. At 254 nm, the reactions leading to cerium(IV) reduction are caused mainly by the OH radical, but approximately 35% of the oxidizing radicals formed in the primary photochemical reaction are SO4-. Cerium(III) species, excited at 254 nm, transfer energy to cerium(IV) and this results in an additional yield of OH and SO4- radicals. Fluorescence measurements confirmed the efficiency of the energy transfer reaction. The ratio of rate constants, k(OH+CeIII)/k(OH+HCOOH), is 2.22 � 0.18 and ф(CeIV*) and ф(CelIII*) giving oxidizing radicals are 0.116 � 0.010 and 0.0083 � 0.0008 respectively. Thus about 5 times more total oxidizing radicals are produced from excited cerium(IV) species at 254 nm than at 365 nm.

scholarly journals Peroxy radical chemistry and OH radical production during the NO<sub>3</sub>-initiated oxidation of isoprene

2012 ◽  
Vol 12 (1) ◽  
pp. 2259-2302 ◽  
Author(s):  
A. J. Kwan ◽  
A. W. H. Chan ◽  
N. L. Ng ◽  
H. G. Kjaergaard ◽  
J. H. Seinfeld ◽  
...  
Keyword(s):  
Chemical Ionization ◽  
Branching Ratio ◽  
Peroxy Radical ◽  
Radical Reactions ◽  
Ionization Mass ◽  
Oh Radical ◽  
Peroxy Radicals ◽  
Radical Production ◽  
Mass Spectrometry Technique ◽  
Spectrometry Technique

Abstract. Peroxy radical reactions (RO2 + RO2) from the NO3-initiated oxidation of isoprene are studied with both gas chromatography and a chemical ionization mass spectrometry technique that allows for more specific speciation of products than in previous studies of this system. We find high nitrate yields (>~80%), consistent with other studies. We further see evidence of significant hydroxyl radical (OH) formation in this system, which we propose comes from RO2 + HO2 reactions with a yield of ~42–62%. An additional OH source is the second generation oxidation of the nitrooxyhydroperoxide, which produces OH and a dinitrooxyepoxide with a yield of ~35%. The branching ratio of the radical propagating, carbonyl- and alcohol-forming, and dimer-forming channels of the RO2 + RO2 reaction are found to be ~18–38%, ~59–77%, and ~3–4%, respectively. HO2 formation in this system is lower than has been previously assumed. Addition of RO2 to isoprene is suggested as a possible route to the formation of several isoprene dimer compounds (ROOR). The nitrooxy, allylic, and C5 peroxy radicals present in this system exhibit different behavior than the limited suite of peroxy radicals that have been studied to date.

scholarly journals Peroxy radical chemistry and OH radical production during the NO3-initiated oxidation of isoprene

2012 ◽  
Vol 12 (16) ◽  
pp. 7499-7515 ◽  
Author(s):  
A. J. Kwan ◽  
A. W. H. Chan ◽  
N. L. Ng ◽  
H. G. Kjaergaard ◽  
J. H. Seinfeld ◽  
...  
Keyword(s):  
Chemical Ionization ◽  
Branching Ratio ◽  
Peroxy Radical ◽  
Organic Peroxide ◽  
Ionization Mass ◽  
Oh Radical ◽  
Peroxy Radicals ◽  
Radical Production ◽  
Mass Spectrometry Technique ◽  
Spectrometry Technique

Abstract. Peroxy radical reactions (RO2 + RO2) from the NO3-initiated oxidation of isoprene are studied with both gas chromatography and a chemical ionization mass spectrometry technique that allows for more specific speciation of products than in previous studies of this system. We find high nitrate yields (~ 80%), consistent with other studies. We further see evidence of significant hydroxyl radical (OH) formation in this system, which we propose comes from RO2 + HO2 reactions with a yield of ~38–58%. An additional OH source is the second generation oxidation of the nitrooxyhydroperoxide, which produces OH and a dinitrooxyepoxide with a yield of ~35%. The branching ratio of the radical propagating, carbonyl- and alcohol-forming, and organic peroxide-forming channels of the RO2 + RO2 reaction are found to be ~18–38%, ~59–77%, and ~3–4%, respectively. HO2 formation in this system is lower than has been previously assumed. Addition of RO2 to isoprene is suggested as a possible route to the formation of several isoprene C10-organic peroxide compounds (ROOR). The nitrooxy, allylic, and C5 peroxy radicals present in this system exhibit different behavior than the limited suite of peroxy radicals that have been studied to date.

scholarly journals A broadband optical cavity spectrometer for measuring weak near-ultraviolet absorption spectra of gases

2011 ◽  
Vol 4 (3) ◽  
pp. 425-436 ◽  
Author(s):  
J. Chen ◽  
D. S. Venables
Keyword(s):  
Absorption Spectra ◽  
Cross Sections ◽  
Optical Cavity ◽  
Absorption Cross ◽  
Enhanced Absorption ◽  
Cavity Enhanced Absorption Spectroscopy ◽  
Near Ultraviolet ◽  
Low Concentrations ◽  
Measured Absorption ◽  
Atmospheric Observations

Abstract. Accurate absorption spectra of gases in the near–ultraviolet (300 to 400 nm) are essential in atmospheric observations and laboratory studies. This paper describes a novel incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for measuring very weak absorption spectra from 335 to 375 nm. The instrument performance was validated against the 3B1-X1A1 transition of SO2. The measured absorption varied linearly with SO2 column density and the resulting spectrum agrees well with published spectra. Using the instrument, we report new absorption cross-sections of O3, acetone, 2-butanone, and 2-pentanone in this spectral region, where literature data diverge considerably. In the absorption minimum between the Huggins and Chappuis bands, our absorption spectra fall at the lower range of reported ozone absorption cross-sections. The spectra of the ketones agree with prior spectra at moderate absorptions, but differ significantly at the limits of other instruments' sensitivity. The collision-induced absorption of the O4 dimer at 360.5 nm was also measured and found to have a maximum cross-section of ca. 4.0×10−46 cm5 molecule−2. We demonstrate the application of the instrument to quantifying low concentrations of the short-lived radical, BrO, in the presence of stronger absorptions from Br2 and O3.

Absolute cross sections and quantum yields for chemiluminescent Al+(1S, 3P) + F2, Cl2 collisions

1988 ◽  
Vol 126 (1) ◽  
pp. 125-135 ◽  
Author(s):  
A. Kowalski ◽  
B. Müller ◽  
Ch. Ottinger
Keyword(s):  
Cross Sections ◽  
Quantum Yields
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