Direkte Untersuchungen der HO_x- und NO_2-Bildung in der Oxidation sauerstoffhaltiger Kohlenwasserstoffradikale unter troposphaerischen Bedingungen Abschlussbericht

Die Oxidation von Kohlenwasserstoffen (KW's) unter NO_x-reichen Bedingungen der Troposphaere fuehrt zur Bildung von Ozon aufgrund der Konversion von NO zu NO_2 durch HO_2/RO_2-Radikalen und die nachfolgende Photolyse von NO_2. Das Ausmass der NO/NO_2-Konversion ist kohlenwasserstoffspezifisch und aendert sich z.B. bei n-Alkanen mit der Kettenlaenge. In dem vorliegenden F+E Vorhaben wurden eine laserspektrometrische Methode entwickelt, die es erlaubt, das Ausmass der NO/NO_2-Konversion fuer einzelne Kohlenwasserstoffe durch Messung von OH und NO_2 direkt zu bestimmen. Die Methode wurde auf C_1-C_6-n-Alkane angewandt. Fuer die einfachsten Alkane (CH_4, C_2H_6, C_3H_8) betraegt #DELTA#NO_2/#DELTA#KW=2.0. Fuer alle hoeheren KW steigt #DELTA#NO_2/#delta#KW an. Die Ergebnisse erlauben die Herleitung von parametrisierten, gekuerzten Mechanismen fuer die Beschreibung der O_3-Bildung in Modellrechnungen und die Herleitung von Ozonbildungspotentialen. (orig.)The oxidation of hydrocarbons in the troposphere under NO_x rich conditions is associated with ozone formation via conversion of NO to NO_2 in reactions with HO_2/RO_2 in the subsequent photolysis of NO_2. The extent of NO/NO_2 conversion is hydrocarbon specific and changes with i.e. chain length in the case of n-alkanes. In the present project a laser spectrometric techniques has been developed which allows the direct determination of NO/NO_2 conversion by measurements of OH and NO_2 growth in the oxidation of individual hydrocarbons. This technique has been applied to all n-alkanes up to n-hexane. It is found that for the simplest alkanes (CH_4, C_2H_6, C_3H_8) #DELTA#NO_2/#DELTA#h.c. equals 2.0. For all larger alkanes #DELTA#NO_2/#DELTA#h.c. increases. These results provide the basis for the derivation of parameterized, lumped mechanistic expressions for the description of ozone formation in chemical/dynamical modells as well as the delineation of ozone formation potentials of individual hydrocarbons. (orig.)SIGLEAvailable from TIB Hannover: F93B923+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Untersuchung der Abbaugeschwindigkeit ausgewaehlter Referenzchemikalien in der Troposphaere Schlussbericht

With 36 refs., 4 tabs., 37 figs.SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Erstellung einer Nahinfrarot-Datei von digitalen Fourier-Transform-Spektren Schlussbericht

Available from TIB Hannover: D.Dt.F. AC 1000(45,10) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Messung der troposphaerischen OH-Konzentration im Bodennahbereich durch UV-Laser-Absorption Abschlussbericht

With 36 refs., 35 figs.Copy held by UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Photochemie mit Lasern Kurzfassungen der Vortraege

SIGLEDEGerman

Entwicklung neuartiger Ethylenhomo- und -copolymerer durch selektive Laser-induzierte Hochdruckpolymerisation

SIGLEAvailable from TIB Hannover: F95B2273+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Bildung und Reaktionen von Oxidantien in fluessiger Phase Abschlussbericht

In the course of the project numerous kinetic, spectroscopic and photochemical parameters for formation processes and reactions of oxidants in aqueous solution have been determined in laboratory investigations. By means of a newly developed laser-photolysis/long-path-laser-absorption experiment kinetic parameters for reactions of the nitrate radical in aqueous solution have been determined. It was found that not only temperature, but also pH and ionic strength strongly influence the rate of degradation of common cloudwater constituents. This finding is of importance because tropospheric cloud droplets undergo multible condensation-evaporation cycles during their lifetime leading to strong variations with regards to acidity as well as to ionic strength. Absolute quantum yields for the formation of OH radicals in the photolysis of aqueous solutions of NO_3"-, NO_2"- and H_2O_2 were determined at 308 and 351 nm as a function of pH and temperature. OH quantum yields were determined by a radical scavenger technique using the fast reaction between OH and SCN"- leading to the formation of (SCN)_2"- which was analysed by time-resolved visible absorption measurements. In the course of this project partial photolytic lifetimes for nitrate, nitrite and hydrogen peroxide were determined based on the measured quantum yields, the absorption coefficients of the precursors and the actinic flux within cloud droplets. An excimer laser photolysis-broadband-diode array absorption experiment was developed and extensive tests and experiments were performed on the photochemical generation and spectroscopic characterization of OH in aqueous solution. The experimental apparatus developed is a new and versatile instrument for the time- and spectrally- resolved study of aqueous phase reactions of transient species. The apparatus was applied for detailed studies of the UV-Vis absorption spectra of SO_x"-(x = 3,4,5), Cl_2"- and CO_3"-. Furthermore, numerous kinetic parameters for reactions of the fore-mentioned radical anions were derived. (orig.)SIGLEAvailable from TIB Hannover: F95B792+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Structural changes accompanying the hydrogen desorption from the diamond C(111):H(1 x 1)-surface revisited by helium atom scattering

The structural phase diagram of the hydrogen terminated diamond-(111) surface, which is of considerable relevance with regard to the low-pressure synthesis of diamond, has been investigated by helium atom scattering and, to allow a comparison to previous work, by low energy electron diffraction. The phase transition to the well-known hydrogen-free (2 x 1) #pi#-bonded chain structure was observed to occur at 990 K, significantly below the previously reported temperature of 1250 K. An analysis of the temporal variation of the He-atom reflectivity for different substrate temperatures allows extraction of the kinetic parameters for the desorption process. (orig.)Available from TIB Hannover: RR 1606(98-03) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

MRD-CI potential calculations: (1) H-O-H ground state and excited states. (2) K-HF ground state

SIGLEAvailable from TIB Hannover: RA 1396(1989,14) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Dynamics of the H+O_2 #->#O+OH chain-branching reaction: Accurate quantum mechanical and experimental absolute reaction cross sections

Available from TIB Hannover: RR 1606(2000,42) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman