Thermochemistry of the R−O<sub>2</sub> Bond in Alkyl and Chloroalkyl Peroxy Radicals

Knyazev, Vadim D.; Slagle, Irene R.

doi:10.1021/jp9726091

Cited by 150 publications

(192 citation statements)

References 32 publications

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“…The thermodynamic properties for the relevant radicals and stable parents were based on the group additivity method of Benson [42] using THERM [43,44] with updated H/C/O groups and bond dissociation groups [44]. We have updated the H/C/O and bond dissociation group values based on the recent studies of Lay and Bozzelli [45] and have modified these slightly so that the thermodynamic functions of Ṙ ϩ O 2 º RȮ 2 reactions agree with the experimental and calculated values of Knyazev and Slagle [46] for ethyl radical. These comparisons can been found in a paper by Curran et al [47].…”

Section: Model Formulationmentioning

confidence: 99%

A comprehensive modeling study of iso-octane oxidation

Curran

2002

Combustion and Flame

1,237

722

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A detailed chemical kinetic mechanism has been developed and used to study the oxidation of iso-octane in a jet-stirred reactor, flow reactors, shock tubes and in a motored engine. Over the series of experiments investigated, the initial pressure ranged from 1 to 45 atm, the temperature from 550 K to 1700 K, the equivalence ratio from 0.3 to 1.5, with nitrogen-argon dilution from 70% to 99%. This range of physical conditions, together with the measurements of ignition delay time and concentrations, provide a broad-ranging test of the chemical kinetic mechanism. This mechanism was based on our previous modeling of alkane combustion and, in particular, on our study of the oxidation of n-heptane. Experimental results of ignition behind reflected shock waves were used to develop and validate the predictive capability of the reaction mechanism at both low and high temperatures. Moreover, species' concentrations from flow reactors and a jet-stirred reactor were used to help complement and refine the low and intermediate temperature portions of the reaction mechanism, leading to good predictions of intermediate products in most cases. In addition, a sensitivity analysis was performed for each of the combustion environments in an attempt to identify the most important reactions under the relevant conditions of study.

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Section: Model Formulationmentioning

confidence: 99%

A comprehensive modeling study of iso-octane oxidation

Curran

2002

Combustion and Flame

1,237

722

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“…3 and 4). h Updated heats of formation for IO, OIO, and CH 3 O 2 (Dooley et al, 2008;Gómez Martín and Plane, 2009;Knyazev and Slagle, 1998) show that the only accessible exothermic product channel of CH 3 O 2 + IO (Drougas and Kosmas, 2007) is CH 3 O + I + O 2 ( H r = −5 ± 6 kJ mol −1 ), consistent with the high yield of I and low yield of OIO found experimentally (Bale et al, 2005;Enami et al, 2006). Sensitivity studies have been carried out using the preferred rate constant for this reaction of 2 × 10 −12 cm 3 molecule −1 s −1 (Dillon et al, 2006b), resulting in an enhancement of the ozone loss of 0.5% in the MBL and of less than 0.1% integrated throughout the troposphere in the J IxOy scenario, and similarly negligible enhancements in the Base scenario.…”

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confidence: 99%

Iodine chemistry in the troposphere and its effect on ozone

et al. 2014

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Abstract. Despite the potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain almost unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of I x O y oxides (i.e. I 2 O 2 , I 2 O 3 and I 2 O 4 ) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15-0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (∼11-14 km) at the equator and extends to the sub-tropics (30 • N-30 • S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ∼20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IO x Loss ) is 2-5 times larger than the combined bromine and chlorine cycles. When I x O y photolysis is included, IO x Loss represents an upper limit of approximately 27, 14 and 27 % of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively, while the lower limit throughout the tropical troposphere is ∼9 %. Our results indicate that iodine is the second strongest ozone-depleting family throughout the global marine UT and in the tropical MBL.We suggest that (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.

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“…[34,44] Finally, it is worth mentioning that pyrene systems proved to be as photo-unstable in other non-halogenated solvents, such as THF (high pyrene photodegradation after 30 min of UV-A irradiation, spectrum not shown), as in chloroform.…”

Section: Photostability Studies Of the Pyrene Systems Under Uv-a-lampmentioning

confidence: 99%

Further Insight into the Photostability of the Pyrene Fluorophore in Halogenated Solvents

et al. 2012

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Pyrene fluorophores of pyrene-functionalized CdSe quantum dots (QD@Py), as well as alkylpyrene and pyrene itself (Py), undergo fast degradation in aerated chloroform under ultraviolet-A (UV-A, 316<λ<400 nm) illumination. Steady-state fluorescence studies of irradiated chloroform solutions of QD@Py show formation of new bands, red-shifted compared to that of the pyrene moiety. Similar behaviour is observed for pyrene and the alkylpyrene system. Column chromatography of the pyrene photolysate in chloroform allowed us to isolate photoproducts arising from pyrene degradation, and to obtain information on the structure of the photoproducts responsible for the emission bands. The most predominant photoproducts were those originating from the reaction of pyrene with dichloromethyl radicals. The phototransformation of QD@Py and the alkylpyrene involves mainly detachment of the alkyl chain from the aromatic ring, induced also by dichloromethyl radicals, and oxidation of the alkyl chain at the benzylic position was detected as well. By contrast, these pyrene systems show a high photostability in aerated dichloromethane. Transient absorption measurements showed formation of both pyrene triplet and pyrene radical cation for all pyrene systems in these halogenated solvents. The yield of pyrene radical cations for Py is higher than for QD@Py and the alkylpyrene. In addition, pyrene radical cations were longer-lived in dichloromethane than in chloroform. The reason for the pyrene photostability in dichloromethane is the different reactivity of chloromethyl and dichloromethyl radicals towards pyrene and oxygen. These studies show that the use of dichloromethane can be a suitable alternative to chloroform when the good solubility properties of these halogenated solvents are needed to dissolve pyrene when this chromophore is used as a fluorescent probe.

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Thermochemistry of the R−O₂ Bond in Alkyl and Chloroalkyl Peroxy Radicals

Cited by 150 publications

References 32 publications

A comprehensive modeling study of iso-octane oxidation

A comprehensive modeling study of iso-octane oxidation

Iodine chemistry in the troposphere and its effect on ozone

Further Insight into the Photostability of the Pyrene Fluorophore in Halogenated Solvents

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Thermochemistry of the R−O2 Bond in Alkyl and Chloroalkyl Peroxy Radicals

Cited by 150 publications

References 32 publications

A comprehensive modeling study of iso-octane oxidation

A comprehensive modeling study of iso-octane oxidation

Iodine chemistry in the troposphere and its effect on ozone

Further Insight into the Photostability of the Pyrene Fluorophore in Halogenated Solvents

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Product

Resources

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Thermochemistry of the R−O₂ Bond in Alkyl and Chloroalkyl Peroxy Radicals