W. Hack

Kinetics of the reaction of hydroxyl radicals with ethylene and with C3 hydrocarbons

The rates of reaction of hydroxyl radicals with ethylene, propane, propylene, methylacetylene, and allene have been measured at room temperature in a discharge-flow system using electron spin resonance detection. The stoichiometries (n=Δ[OH]/Δ[R]) were obtained by mass spectrometric analysis of the reacted gas under similar, although not completely identical conditions. The primary rate constants for the C3-hydrocarbons obtained by combining the two are given as: OH + propane k6=(5.0 ± 1.0)× 1011 cm3 mol–1 s–1+ propylene k7=(3.0 ± 1.0)× 1012 cm3 mol–1 s–1+ methylacetylene k8=(5.7 ± 1.0)× 1011 cm3 mol–1 s–1+ allene k9=(2.7 ± 1.5)× 1012 cm3 mol–1 s–1. The values of n as well as the nature of the products provide some information on the mechanisms involved.A value of k5=(1 ± 0.3)× 1012 cm3 mol–1 s–1 was obtained for the reaction of OH + ethylene.

Reaction rates of NH2-radicals with NO, NO2, C2H2, C2H4 and other hydrocarbons

Absolute rate constants for gas phase reactions of NH2 radicals with nitrogen dioxide, nitric oxide, acetylene and ethylene have been determined in a discharge flow system with laser-induced resonance fluorescence detection of NH2. The radicals were produced by the fast reaction F+NH3. The kinetic measurements were performed in the temperature range 209≤T≤505 K at pressures of one torr He as the main carrier gas. The following rate constants were obtained: k N O 2 + N H 2 ( T ) = 1.9 ⋅ 10 20 ⋅ T − 3.0 [ c m 3 / mol sec ] k NO + N H 2 ( T ) = 2.7 ⋅ 10 17 ⋅ T − 1.85 [ c m 3 / mol sec ] k C 2 H 2 + N H 2 ( T ) = 1.42 ⋅ 10 16 ⋅ T − 2.7 [ c m 3 / mol sec ] The rate constant for the reaction of C2H4 with NH2 shows little temperature dependence kC2H4+NH2(T)=1.3·109 [cm3/mol sec]. The reactions of NH2 with allene and propylene are slow. The measurements lead to the upper limits kC3H4+NH2≤5·108 [cm3/mol sec] and kC3H6+NH2≤6·108 [cm3/mol sec] at room temperature.

Direct studies of elementary reactions of NH2-radicals in the gas phase

Elementary reactions of the NH 2 -radicals have been studied in discharge flow systems with LMR (NH 2 , NH, OH, O, HO 2 ), ESR (H, D, O, OH) and LIF (NH 2 , NH, OH, HNO) detection methods. The NH 2 radicals were produced by the reaction F+NH 3 →NH 2 +HF and the following rate constants were measured: NH 2 +NH 2 →NH+NH 3 (1a) k 1a (296 K)≤2·10 9 cm 3 /mol s NH 2 +NH→products (2) k 2 (296 K)=(8±3) 10 3 cm 3 /mol s NH 2 +D→NHD+H (3) k 3 (296 K)=(3.2±0.8) 10 3 cm 3 /mol s NH 2 +O→products (4) k 4 (296 K)=(5.3±1.5) 10 3 cm 3 /mol s →HNO+H (4c) k 4c (296 K)=(4.6±1.2) 10 13 cm 3 /mol s →NH+OH (4d) k 4d (296 K)=(7±3) 10 12 cm 3 /mol s NH 2 +iso−C 4 H 10 (5) k 5 (T)=1.9·10 11 exp(−19.8 kJ/mol −1 /RT) cm 3 /mol s

Elementary reactions of electronically excited N2 in the A 3Σu+ state with H2 and NH3

Abstract The reactions of N 2 (A 3 Σ u + (ν′)) with H 2 (X 1 Σ g + ) and NH 3 (X 1 A 1 ) have been studied in a fast discharge flow system. The metastable N 2 (A) molecules were produced by the energy transfer reaction with Ar( 3 P 2.0 ). N 2 (A(ν′)) was detected by laser-induced fluorescence via the transition (B 3 Π g -A 3 Σ u + ). The measured rate constants for the reactions N 2 (A 3 Σ u + (0⩽ν′⩽3)) + H 2 (X 1 Σ g + ) → products are: k 1 0 = 2.3, k 1′ = 13, k 1″ = 14 and k 1‴ = 15 (in 10 9 cm 3 mol −1 s −1 for ν′ = 0, 1, 2, and 3) at room temperature. The main products are H( 2 S) atoms. The room temperature rate constants for the reaction N 2 (A 3 Σ u + (0⩽ν′⩽3)) + NH 3 (X 1 A 1 ) → products are: k 2 0 = 8.2, k 2′ = 9.2, k 2″ = 11 and k 2‴ = 14 (in 10 13 cm 3 mol −1 s-−1 for ν′ = 0, 1, 2 and 3). The products of the latter reaction are NH 2 (X 2 B 1 ), NH (X 3 Σ − ) radicals and H ( 2 S) atoms. The mechanisms of the above reactions are discussed.

Far-infrared laser magnetic resonance spectra of vibrationally excited OH and OD

Several new far-infrared laser magnetic resonance spectra of OH and OD have been detected in the reactions of H or D atoms with ozone. The strongest spectra have been assigned to rotational transitions in v= 6 OH and v= 4 OD of the X2Π3/2 state.

Experimente zur elastischen Streuung von Kaliumatomen (2S1/2) an Jodatomen (2P3/2) in gekreuzten Molekularstrahlen

Der differentielle und totale Streuquerschnitt von 2S1/2 Kaliumatomen an 2P3/2 Jodatomen wurde in gekreuzten Molekularstrahlen bei thermischen Relativenergien gemessen. Im Bereich von Ablenkwinkeln δ < 2° wurden Maxima des differentiellen Streuquerschnittes gefunden, die sich über die klassische Regenbogenstreuung deuten lassen. Messungen des totalen Streuquerschnittes bei Relativgeschwindigkeiten von 0,5 bis 1,8-105 cm/sec zeigen eine Abhängigkeit von der Geschwindigkeit, wie sie für die van der Waals Anziehung charakteristisch ist. Für höhere Relativgeschwindigkeiten wurden Abweichungen beobachtet, die sich dadurch deuten lassen, daß die Streuung am abstoßenden Teil der Wechselwirkungspotentiale den Verlauf des totalen Streuquerschnittes maßgeblich beeinflußt. Für die Potentialtöpfe der angeregten kovalenten Elektronenzustände des KJ ergibt sich mit dieser Deutung εΩ= 1 ≈3,3 · 10-3 eV, εΩ= 0+, 0-, 2 ≈ 2,5 · 10-3 eV. εΩ= 0+, 0-, 2 ≈ 1,9 · 10-3 eV.

Detailed kinetic studies on elementary NH2-reactions

The NH2(2B1) reactions: NH2+D2→NH2D+D (R1) NH2+H2O→NH3+OH (R2) and the reverse reaction: OH+NH2→NH2+H2O (R3) have been measured directly in an insothermal discharge flow system at pressures in the range 1.3≦p/m bar≦4.0 with He as the main carrier gas. NH2 and OH were produced in the reaction of F atoms with NH3 and H2O respectively. Laser induced fluorescence (LIF) detection was used to follow the OH and NH2 radical concentrations as a function of the position of movable probes. For Rxn. (R1) kinetic data were obtained by following the [NH2] profiles under pseudo first order conditions [NH2]0≪[D2]0 in the temperature range 639≦T/K≦1140. k1(T) is represented by the following Arrhenius-expression: k1(T)=2.9·1012 exp(−47.6±2 kJ mol−1/RT) [cm3 mol−1 s−1] Direct measurements for the kinetic isotope effect resulted in k1(H2)/k1(D2)=3.3 at 740 K and 2.4 at 1140 K. Ab initio energy surfaces calculated with the CEPA-method were used to discuss the kinetic isotope effect in comparison to NH2+H2 in relation to tunnel corrections. For Rxn. (R2), the rate constant k2(1000 K)=6·109 cm3 mol−1 was obtained experimentally. The comparison with k2(T), calculated from the reverse reaction at 1000 K, confirmed the value of 192 kJ mol−1 for the heat of formation of NH2.

Direct measurements of the reaction NH2+CH4→NH3+CH3 in temperature range 743≤T/K≤1023

The reaction N H 2 + C H 4 → N H 3 + C H 3 ( 1 ) was studied in an isothermal discharge flow system over the temperature range 743≤T/K≤1023 at a pressure of p=4.0 mbar with He as the main carrier gas. The [NH2](t) profiles were followed under pseudo first order conditions [CH4]0≫[NH2]0 by laser induced fluorescence. The rate constant is given by the Arrhenius expression: k 1 ( T ) = 5.8 ⋅ 10 12 exp ⁡ ( − ( 55.1 ± 6 ) k J mol − 1 / R T ) c m 3 mol − 1 s − 1 in the above given temperature range. The result is discussed in relation to other hydrogen abstraction reactions of NH2 from saturated hydrocarbons.

Methoden zur Bestimmung von Radikal-Zuständen und -Konzentrationen in der Gasphase — Eine Übersicht

SummaryDetection methods for atoms and radicals are described with respect to the range of specific and sensitive application. In one table detection methods for about 26 atoms and 48 radicals are listed. In a second table detection methods applied to detect C-atoms and radicals containing either one or two C-atoms and C3-radicals are summarized. In the tables recent kinetic applications of the various methods are cited.ZusammenfassungNachweismethoden für Atome und Radikale im Hinblick auf verschiedene kinetische Anwendungen werden charakterisiert. Als wesentliche Kriterien zur Beurteilung der Methode werden die Eigenschaften Universalität, Spezifität und Empfindlichkeit herangezogen. In einer Tabelle werden für etwa 26 Atome und 48 Radikale und in einer anderen für C-Atome und etwa 44 Radikale, die entweder ein oder zwei C-Atome enthalten, und C3-Radikale Nachweisverfahren zusammengestellt. In der Tabelle sind auch gegebenenfalls neuere Anwendungen in kinetischen Experimenten zitiert.