Author: Emmanuel Assaf
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The hydroxyl radical OH and hydroperoxy radical HO2 radicals are key species in many oxidation processes in the atmosphere. The degradation of volatile organic compounds under tropospheric conditions is induced by reactions with hydroxyl radicals followed by the subsequent chemistry of the initial OH oxidation products with O2. This thesis was focused on the kinetic study of some of these atmospherically relevant reactions to better understand their oxidation mechanisms using an experimental system of laser photolysis coupled to Laser Induced Fluorescence (LIF, for OH radical) and continuous-wave Cavity Ring-Down Spectroscopy (cw-CRDS, for OH, HO2 and RO2 radicals) detection techniques. After determining the infrared spectrum of OH, HO2 and CH3O2 radicals in the near infrared region and the absorption cross-sections of few selected lines, four systems were studied with the above mentioned techniques: CH3O2 + OH, C2H5O2 + OH, C3H7O2 + OH and C4H9O2 + OH. The rate constant and the HO2 yield of the four reactions were determined. In addition, the rate constants of few secondary reactions such as CH3O + HO2, CH3O + CH3O or OH + HO2 have been determined.
Author: Cornelie Bänsch
Publisher: Logos Verlag Berlin GmbH
ISBN: 3832546324
Category : Science
Languages : en
Pages : 196
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Hydroxyl radicals (OH) play a key role in ignition processes and in the atmosphere. Thus, the detailed knowledge of the kinetics of OH reactions is crucial in combustion and atmospheric research. In this work, an experimental approach for time-resolved studies of OH radical reactions at high pressures with pulsed laser photolysis/laser-induced fluorescence was revised and the reactions of dimethyl ether, diethyl ether, and dimethoxymethane with OH radicals were investigated in detail. The results reveal a deeper insight into the reaction processes of ether compounds with OH in general, contributing to a better understanding of the combustion of different biofuels and fuel additives.
Author: Chaithanya D. Jain
Publisher:
ISBN:
Category :
Languages : ab
Pages : 172
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OH and HO2 radicals play a vital role in many oxidation processes in the atmosphere. The degradation of volatile organic compounds under tropospheric conditions is generally induced by the reaction with hydroxyl radicals, followed by reaction with oxygen. This thesis involved the study of the mechanisms and reaction pathways of some of these reactions using an experimental system of laser photolysis coupled to Laser Induced Fluorescence (LIF, for OH) and continuous wave Cavity Ring-Down Spectroscopy (cw-CRDS, for HO2) detection techniques. The coupling of these detection techniques allowed studying the simultaneous, time resolved kinetics of OH and HO2 radicals and spectroscopic measurements for different species by the cw-CRDS technique. Different chemical systems studied using the above experimental technique include: 1) kinetics of the reaction of OH radicals with CH3OH and CD3OD, 2) HO2 yield in the OH-initiated oxidation of SO2, 3) an energy dependence study on the direct formation of HO2 radicals from the photoexcitation (at 248 nm) of various aromatic hydrocarbons (benzene, toluene, xylene or mesitylene) in the presence of oxygen. In addition the spectroscopic applications of the cw-CRDS technique have been used to measure the absorption cross-sections of selected absorption lines of H2O2, HONO, HO2 and DO2 in the near infrared region.
Author: Pranay P. Morajkar
Publisher:
ISBN:
Category :
Languages : en
Pages : 154
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OH and HO2 radicals play a vital role in many oxidation processes in the atmosphere. Thedegradation of volatile organic compounds under tropospheric conditions is induced by reaction withhydroxyl radicals followed by the subsequent chemistry of the initial OH oxidation products with O2.This thesis deals with the kinetic study of some of these atmospherically relevant reactions to betterunderstand their oxidation mechanisms using experimental techniques such as laser photolysiscoupled to detection by Laser Induced Fluorescence (LIF, for OH), continuous wave- Cavity RingdownSpectroscopy (cw-CRDS, for HO2) and time resolved UV spectroscopy (UV, forHexamethylbenzene-OH adduct). Different chemical systems have been studied using the above techniques: 1) the reaction ofHO2 radicals with formaldehyde, 2) the 248 nm photolysis of acetaldehyde and 3) the OH initiatedoxidation of Hexamethyl benzene. In addition to this, the spectroscopic application of cw-CRDStechnique and UV spectroscopy has been used for the measurement of absorption cross section ofselected absorption lines of formaldehyde in the near infrared region and Hexamethylbenzene-OHadduct in the UV region respectively.
Author: Xiaoying Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 498
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Author: Zhijun Zhao
Publisher:
ISBN:
Category : Dynamics
Languages : en
Pages :
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Radical reactions play central roles in regulating regional air quality and global climate. Some potentially important gas phase radical reactions are being investigated in this research project, including Cl reactions with acetone, butanone, 3-pentanone, pyridine, and dimethyl selenide (DMSe), HO2 complex formation and dissociation with formic and acetic acids, and reactive and non-reactive quenching of O(1D) by the potent greenhouse gases SO2F2, NF3, and SF5CF3. The involved radicals are generated by laser flash photolysis (LFP). Temporal profiles of either the radical reactant or a product are monitored in "real time" using atomic resonance fluorescence spectroscopy (RF), time-resolved UV-visible absorption spectroscopy (TRUVVAS), or tunable diode laser absorption spectroscopy (TDLAS), allowing kinetic and mechanistic information of these reactions to be obtained. These studies provide new knowledge of the investigated radical reactions and facilitate a better understanding of their significance in atmospheric chemistry.
Author: Chao Yan
Publisher:
ISBN:
Category :
Languages : en
Pages : 198
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The kinetics of several free radical-radical reactions was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 292 – 714 K temperature range and the 1- 100 bar pressure range. Free radicals such as CH3, OH and Cl are generated by photodissociation of parent molecules; some other radicals such as CH3O2 and HO2 are generated in secondary reactions following the initial photodissociation. Different free radicals are monitored at different wavelengths depending on their UV absorption spectra. Quantitative measurements of the concentrations of free radicals relay upon the absolute intensity of photolysis laser light determined by well characterized in situ actinometry. Experimental temporal absorption profiles are fitted by numerical solutions of a system of differential equations (ODE) which correspond to the reaction mechanism.
Author: Koji Miyazaki
Publisher:
ISBN:
Category :
Languages : en
Pages : 89
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Peroxy radicals RO2 (with R = H or CxHy) play an important role in the photo-oxidation cycles of the troposphere. They are produced mainly via the atmospheric oxidation of hydrocarbons and carbon monoxide by OH radicals and subsequent reactions with O2. They can further react with NO to produce NO2, witch is an important reaction of tropospheric ozone generation. To understand the mechanism of this tropospheric ozone generation, precise and accurate measurements of ambient peroxy radical concentrations are essential. And not only atmospheric concentration measurements but also atmospheric kinetics studies such as lifetime measurements of peroxy radicals are necessary. Recent publications show big differences between measured peroxy radical concentrations and those calculated with chemical models. These could be caused by missing reaction pathways and uncertainties in reaction yields and rate constants. To investigate these missing reactions and the uncertainties in known peroxy radical reactions via ambient measurements, newly developed two instruments as described below are applied. One is a technique for the selective measurement of atmospheric peroxy radical concentrations of HO2 and RO2 using the PERCA technique. HO2 radicals are selectively removed by using a glass denuder to achieve the selective measurement. The other one is a technique for total HO2 loss rate measurement in the atmosphere by using laser-flash photolysis and LIF detection of HO2. Generated HO2 radicals by laser-flash photolysis react with ambient reactive species such as NOX in the reaction tube. HO2 loss is measured using LIF at 308 nm coupled with chemical conversion with NO.
Author: Yong Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 404
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Author: Rafal Strekowski
Publisher:
ISBN:
Category : Hydrocyanic acid
Languages : en
Pages : 380
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