Description: Das Projekt "Struktur-Wirkung-Beziehungen fuer Reaktionen waehrend des Abbaus von biogenen leichtfluechtigen Kohlenwasserstoffen" wird vom Umweltbundesamt gefördert und von Universität-Gesamthochschule Essen, Fachbereich 8 Chemie, Institut für Physikalische und Theoretische Chemie durchgeführt. In the present project the oxidation reactions will be initiated via the photolytic production of OH radicals or by photolysis of specific alkylhalides in the presence of O2 and NO. The RO reactivity can be related to the time dependence of (OH) and (NO2) which are monitored simultaneously using laser spectroscopic methods. The technique has already been validated. During this project it will be extended to investigate C3, C4 and C5 alkoxy radicals. The method will provide information on all over-all reactivities of alkoxy radicals generated in the OH initiated oxidation of the alkanes mentioned above, and is therefore useful in deriving absolute information on the NO2 (and therefore O3) yield per hydrocarbon oxidized to a carbonyl compound under tropospheric conditions (NOCON factors). Moreover, in a detailed analysis of the (NO2) and (OH) data, making use of infomation on the position of the initial OH attack and using different isomers of the alkane, reactivities of specific RO radicals will be obtained. The experiments will be performed under variation of (O2) and (NO) leading to a determination of the erlative importance of nitrit formation versus decomposition/isomerisation and reaction with O2. Moreover, the effect of the variation of total pressure (10-100 mbar) in the decomposition and isomerisation rate coefficients will be investigated. Theoretical studies of the unimolecular isomerisation and decomposition will be performed using RRKM methods. A major information essential for the performance of these calculations ist the thermochemistry of the different reaction pathways. Starting from detailed knowledge of the C2 and C3 systems a semiempirical extrapolation method is developed for extracting the reaction enthalpies as a function of the chain length of the RO radical. Moreover, intrinsic activation barries for the decomposition and isomerisation reactions of different RO radicals are extracted using ab inition calculations on RO radical geometries using GAUSSIAN programme. The results of these calculations will be compared with experimental data where those are available with reasonably high reliability (C2-C5). Data from the experimental and theoretical studies by the various memebers of this work package will be used to develop SARs for alkoxy reactions. So far our group has made preliminary inverstigations for the n-alkanes up to the C6 system. The results obtained represent weighted averages for the different individual members of alkoxy that are formed in the oxidation of larger alkanes as a result of different CI and OH attack. They indicate that the rate coefficients of RO decomposition or isomerisation approach a limiting value of 10(xp=5) 1/s at room temperature and 50 mbar total pressure.
Types:
SupportProgram
Origin: /Bund/UBA/UFORDAT
Tags: Alkan ? Ozon ? Nitrit ? Alicyclischer Kohlenwasserstoff ? Arsen ? Kohlenwasserstoff ? VOC ? Laser ? Laserspektroskopie ? Stickstoffdioxid ? Photolyse ? Struktur-Wirkung-Beziehung ? Daten ? Hochrechnung ? Isomer ? Oxidation ? Studie ? Abbau ? Atmosphäre ? Atmosphärenchemie ? Grenzwert ? Reaktionskinetik ? Verpackung ? Radikal [Chemie] ? SARBVOC ? free radicals ? kinetics ? laser-spectroscopy ?
Region: Nordrhein-Westfalen
Bounding box: 6.76339° .. 6.76339° x 51.21895° .. 51.21895°
License: cc-by-nc-nd/4.0
Language: Deutsch
Time ranges: 1996-06-01 - 1998-05-31
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