H. Gg. Wagner

Kinetics of the reaction HOCO+O2 in the gas phase

Using the discharge flow method, the kinetics of the gas phase reaction HOCO + O2 products (1) was investigated at room temperature and pressures around p ≈ 2.0 mbar with Far Infrared LaserMagnetic Resonance (FIR-LMR) detection of HOCO, HO2 , and OH. From the measured concentration-versus-time decay profiles of HOCO in the absence and presence of a large excess of O2 , theoverall rate constant of the reaction was found to be k1 (296 K) = (9.9 ±1.5) • 1011 cm3/mol • s. The main reaction channel, which leads to production of HO2 + CO2 , could be established.

Comparative study of the reactions of 16OH and 18OH with H16O2

The gas phase reactions 18OH + H16O2 → H218O + 16O2 (1a) 18OH + H16O2 → 16OH + H18O16O (1b) were studied at room temperature in a discharge flow reactor with far infrared laser magnetic resonance (LMR) detection of 16OH, 18OH and H16O16O. The formation of 16OH in the course of the reaction was observed. The absolute rate constant for the overall removal of 18OH in excess of H16O16O was determined. Each run was accompanied by a control experiment replacing the initial 18OH by the same amount of 16OH. From these experiments a branching ratio is obtained of k1a/( k1a + k1b) = 0.52 ± 0.08

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.

Untersuchung des thermischen Zerfalls von N2O in Stoßwellen

Der thermische Zerfall von N2O hinter reflektierten Stoßwellen wurde zwischen 1500 und 2500 °K in Argon als Trägergas untersucht. Der Konzentrationsverlauf von N2O wurde mit einem photoelektrischen Verfahren über die Absorption bei 2300 Å verfolgt. Gleichzeitig damit konnte über die Absorption bei 2260 Å die Bildung von NO beobachtet werden. Die im Niederdruckbereich des unimolekularen Zerfalls gemessene Geschwindigkeit der Reaktion N2O ➝·Ν2+O ergab sich zu d[N2O]/dt=-k[M] [N2O] mit k=1015 exp(-E/R T) (cm3 Mol-1 sec-1) (E=61 kcal/Mol und [M] =Gesamtkonzentration).

Far-Infrared Laser Magnetic Resonance Detection of CH2Cl

Abstract New Far Infrared Laser Magnetic Resonance (LMR) spectra have been detected in the reaction of Cl atoms with CH2CO. Based on chemical and kinetic evidence they were assigned to CH2Cl radicals. The assignment was substantiated by subsequent experiments which employed the reactions of F atoms with CH3Cl and Na atoms with CH2Cl2, respectively. The three different sources yielded identical spectra

Messung der Geschwindigkeitskonstanten der Reaktion NH2+CH4→NH3+CH3 hinter einfallenden Stoßwellen / Measurements of the Rate Constant of the Reaction NH2+CH4→NH3+CH3 behind Incident Shock Waves

The rate constant of the reaction NH2+CH4→NH3+CH3 was measured at temperatures of about 1800 K by time-resolved UV-spectroscopy of the products behind incident shock waves. NH2 was produced by the presence and thermal decomposition of hydrazine. The data were evaluated by fitting simulated concentration-time-profiles to the measured ones. A mean rate constant k = (4±2) 1011 cm3 mol-1 s-1 1730 <T/K < 1950 was obtained. The temperature dependence of the reaction is discussed.

The Mercury-Sensitized Photolysis of Pentamethyldisilane

Abstract Two primary processes were observed in the Hg-sensitized photolysis of Me 5 Si 2 H: (I) hydrogen abstraction from the Si-H bond with a quantum yield of 0(1) = 0.85, (V) Si-Si bond breaking with 0(V) = 0.04. The hydrogen atoms formed in (/) undergo an H atom abstraction reaction (k(3)), as well as substitution reactions at the Si centers resulting in the formation of dimethylsilane and trimethylsilyl radical (k(4)) or trimethylsilane and dimethylsilyl radical (k(5)). The following branching ratios have been determined: [xxx] The ratio of disproportionation (k(2)) to combination (k(1)) for the pentamethyldisilyl radical has been determined with MeOH as the scavenger for 1-methyl-l-trimethylsilylsilene, 0.046 < k(2)/ A: C1) < 0.071. A mechanism with pertinent rate constants has been proposed which accounts for the results. Abstract Two primary processes were observed in the Hg-sensitized photolysis of Me 5 Si 2 H: (I) hydrogen abstraction from the Si-H bond with a quantum yield of 0(1) = 0.85, (V) Si-Si bond breaking with 0(V) = 0.04. The hydrogen atoms formed in (/) undergo an H atom abstraction reaction (k(3)), as well as substitution reactions at the Si centers resulting in the formation of dimethylsilane and trimethylsilyl radical (k(4)) or trimethylsilane and dimethylsilyl radical (k(5)). The following branching ratios have been determined: [xxx] The ratio of disproportionation (k(2)) to combination (k(1)) for the pentamethyldisilyl radical has been determined with MeOH as the scavenger for 1-methyl-l-trimethylsilylsilene, 0.046 ≤ k(2)/ k(1) ≤ 0.071. A mechanism with pertinent rate constants has been proposed which accounts for the results.

Reaction of Trimethyl-and Dimethyl-Silyl Radicals with Pentamethyldisilane

Abstract The rate constant for the H atom abstraction of trimethylsilyl radicals from pentamethyldisilane (k(4)) was measured relative to the trimethylsilyl combination reaction k(3). A value for =(8.53 ± 0.08) · 10-11cm3/2s–1/2 was obtained. For the dimethylsilyl radical, a smaller value for the corresponding rate constant ratio (5.9 ± 0.2) · 10-11 cm3/2 s–1/2 was measured, and this was attributed to a disproportionation reaction between the dimethylsilyl and the pentamethyldisilyl radical leading to dimethylsilylene.

About the Radical Formation in the Pyrolysis of Formic Acid at High Temperatures

Abstract The formation of radicals in the HCOOH pyrolysis was investigated in the temperature and density range between 1450 and 2450 K and 2 • 10-6 and 1.2 • 10-5 mol /cm3, respectively. The small amount of radicals found indicates that a radical forming reaction path in the formic acid pyrolysis is smaller than 0.2% of the total decomposition rate

On the Insertion Reactions of CH2(ã1A1) in to Some Element-Hydrogen Bonds

Absolute values for the removal rates of CH2(ã1A1) by NH3, CH3NH2, CH3OH, HCl, and HF have been determined in the gas phase at low pressures and room temperature. CH2(ã1A1) was generated by pulsed laser photolysis of CH2CO. The measurements were carried out by observing the laser induced fluorescence of 1CH2 after excitation by a pulsed laser as a function of the time delay between the photolysis and analysis pulses. The overall rate constants were found to be 2.4, 2.4, 2.3, 1.6 and 0.13 · 1014 cm3/mol s, respectively. NH2 was shown by LIF detection to be a primary product of the reaction of 1CH2 with NH3. The intersystem crossing channel of 1CH2 was investigated by monitoring the formation of CH2(X̃3B1) with laser magnetic resonance. LMR absorption intensities of 3CH2 resulting from quenching of 1CH2 in the presence and absence of the reactant R were compared under otherwise identical conditions. The branching ratios of quenching versus total removal of 1CH2, turned out to be 0.30, 0.13 and 0.98 for NH3, CH3OH, and HF, respectively.