Download or read book Kinetic Study of Reactions with Interest to Atmospheric Chemistry by Simultaneous Detection of OH and RO2 Radicals Coupled to Laser Photolysis written by Emmanuel Assaf and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Reactions of Hydroxyl Radicals with Oxygenated Hydrocarbons in the Gas Phase A Laser Photolysis Laser Induced Fluorescence Study written by Cornelie Bänsch and published by Logos Verlag Berlin GmbH. This book was released on 2017 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Laser Photolysis Coupled to Detection by LIF and Cw CRDS written by Chaithanya D. Jain and published by . This book was released on 2011 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Application of Laser Photolysis Coupled to Time Resolved Optical Detection Methods to Study the Kinetics and Spectroscopy of Atmospherically Relevant Species written by Pranay P. Morajkar and published by . This book was released on 2012 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Kinetics of Free Radical Reactions Generated by Laser Flash Photolysis of Oh Cl and So4 Cl in the Aqueous Phase chemical Mechanism Kinetics Data and Their Implications written by Xiaoying Yu and published by . This book was released on 2001 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laser Flash Photolysis Studies of Some Gas Phase Reactions of Atmospheric Interest written by Zhijun Zhao and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Kinetic Study of Free Radical radical Reactions of Combustion Importance at Elevated Pressures written by Chao Yan and published by . This book was released on 2018 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Study of the Nature and Roles of Peroxy Radicals in the Atmosphere Towards the Understanding of Oxidant Formation Using Laser flash Photolysis and LIF Detection Technique written by Koji Miyazaki and published by . This book was released on 2012 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Experimental and Theoretical Study of Atmospheric Free Radical Reactions written by Yong Liu and published by . This book was released on 2005 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Addition and Recombination Reactions of Unsaturated Radicals Using a Novel Laser Kinetics Spectrometer written by Huzeifa Ismail and published by . This book was released on 2008 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the construction of a novel, low-noise laser kinetics spectrometer. A quasi-CW (picosecond pulse), tunable Ti:Sapphire laser is used to detect various transient species in laser flash photolysis kinetics experiments via direct absorption. The spectral range of the laser, when used with a harmonic generator, covers most of the visible wavelength region, allowing for the detection of a wide array of organic radical species. Paired with a temperature-and pressure-controlled flow reactor equipped with a Herriott-type optical multiple pass cell, transient absorptions of ~0.0001 can be measured, corresponding to cross section - concentration products of less than 1x10-7 cm". The flexibility and high sensitivity of this instrument allows direct and accurate measurement of many important transient intermediates in combustion and atmospheric chemistry.Using this instrument, we report the self-reaction rate coefficient of vinyl and allyl radicals. Vinyl iodide and allyl iodide are used as precursors to generate respective radicals via laser-flash photolysis at 266 nm. Second order chemical reactions require an accurate determination of the initial radical concentration, which we determined using direct laser absorption by I atom at 1315 nm. The current study finds the self-reaction rate constant for vinyl radical to be more than a factor of two slower than previous studies and allyl self reaction rate constant to be 50% faster than values reported in the literature. The absorption cross sections of the vinyl radical at 404, 423.2, & 445 nm and allyl radical at 404 & 408 nm are also determined. This thesis also reports measurements of rate coefficients for the reaction of vinyl radical with various alkenes: ethylene, propene, isobutene, 1-butene, and 2-butene,performed over a temperature range of 300 K to 700 K at 100 Torr. The measured vinyl radical disappearance rates compare well with ab initio quantum calculations. The combined measurements and calculations provide improved estimates for other vinyl + alkene reactions.
Download or read book Laser Flash Photolysis Studies of O 1D2 and OH X2II Reactions of Atmospheric Interest written by Rafal Strekowski and published by . This book was released on 2001 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Kinetic Studies of Free Radical Reactions with Reference to Atmospheric Chemistry written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Surface Water Photochemistry written by Paola Calza and published by Royal Society of Chemistry. This book was released on 2015-11-20 with total page 310 pages. Available in PDF, EPUB and Kindle. Book excerpt: Borne out of the current widespread interest in the pollution of water bodies, this book explores the latest research concerning the photochemical fate of organic pollutants in surface water. The main objective is to give insight into both the functioning of ecosystems and the behaviour of emerging pollutants in those ecosystems. Particular importance is dedicated to techniques that can be used in the field and in the laboratory for the detection of pollutants and of their transformation intermediates. The inclusion of photochemical processes that have not gained previous coverage will afford the reader novel insights, whilst the focus on modelling and transformation intermediates will ensure the title's relevance to academics, the chemical manufacturing industries and environmental assessment experts alike.
Download or read book The Chemical Dynamics and Kinetics of Small Radicals written by Kopin Liu and published by World Scientific. This book was released on 1995 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights recent progress in the chemistry of radicals. Developments include the growing use of lasers to generate radicals, the application of lasers to provide state, angular, polarization, energy and real-time resolution in kinetics and dynamics experiments, the development of theories for handling the reactions of radicals, and the simulation of the reaction dynamics of increasingly larger systems for direct comparison to experimental results. The book emphasizes the increasing interaction between experimental dynamics, kinetics and theory. It is appropriate for chemistry graduate students and researchers about to enter the field. However, the discussions of some topics progress to a more advanced level so that even an expert will find the book useful.
Download or read book Pulsed Laser Photolysis Kinetics Study of Reactions Between Small Radical Species written by John Michael Nicovich and published by . This book was released on 1993 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Laser Flash Photolysis Studies of Halogen Atom Reactions of Atmospheric Interest written by Patrick L. Laine and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analytical Techniques for Atmospheric Measurement written by Dwayne Heard and published by John Wiley & Sons. This book was released on 2008-04-15 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt: Almost all of the breakthroughs in understanding the atmospherehave been initiated by field observations, using a range ofinstrumental techniques. Developing or deploying instruments tomake further observations demands a thorough understanding of thechemical and spectroscopic principles on which such measurementsdepend. Written as an authoritative guide to the techniques of instrumentalmeasurement for the atmospheric scientist, research student orundergraduate, Analytical Techniques for Atmospheric Measurementfocuses on the instruments used to make real time measurements ofatmospheric gas and aerosol composition. Topics covered include howthey work, their strengths and weaknesses for a particular task,the platforms on which they have been deployed and how they arecalibrated. It explains the fundamental principles upon which theinstrumental techniques are based (ie what property of a moleculecan be exploited to enable its detection), what limits instrumentalsensitivity and accuracy, and the information that can be gainedfrom their use.
