H. Gg. Wagner’s research while affiliated with Max Planck Institute for Informatics and other places

The isotope exchange reactions between ¹⁸ OH and NO, NO 2 , N 2 O and O 2 were studied at room temperature in a discharge flow system with laser magnetic resonance detection of ¹⁸ OH and ¹⁶ OH. Exchange rate constants of where obtained for NO and NO 2 , respectively. Upper limits of k < 1 · 108 cm ³ /mol s can be reported for the reactions The results are compared with recombination rate data in the limit of high pressures and with vibrational deactivation measurements.

Der differentielle und totale Streuquerschnitt von ² S 1/2 Kaliumatomen an ² P 3/2 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 1,8-10 ⁵ 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.

Der thermische Zerfall von N20 hinter reflektierten Stoßwellen wurde zwischen 1500 und 2500 oK in Argon als Trägergas untersucht. Der Konzentrationsverlauf von N20 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 N20→N2 + 0 ergab sich zu d[N20]/dt= -k[M] [N20] mit k = 1015 exp(-E/R T) (cm3 Mol-1 sec-1) (E=61 kcal/Mol und [M] = Gesamtkonzentration).

The reactions of OH and HO 2 , radicals were studied in an isothermal flow reactor using ESR detection technique. The rate of the reaction H + O 2 + M → HO 2 + M (5) with M = He was measured at T = 300 K k 5 = 5 · 10 ¹⁵ cm ⁶ /mol ² sec . Via quantitative measurement of OH-radical concentration by ESR it was shown that the reaction of HO 2 radicals with H-Atoms produces mainly OH-radicals. The reactions OH + H 2 O 2 → HO 2 + H 2 O (6) and NO + HO 2 → NO 2 + OH (7) were studied in the temperature range of 298 ≦ T ≦ 670 K.

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 • 10⁻⁵mol /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. © 1992, Verlag der Zeitschrift für Naturforschung. All rights reserved.

Using crossed nozzle beam technique, the primary products of OH reactions with acetylen and hydrazine were determined without subsequent steps, giving OH + C 2 H 2 → CO + CH 3 , OH + N 2 H 4 → NH 2 O + NH 3 .

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

Absolute values for the removal rates of CH 2 (ã ¹ A 1 ) by NH 3 , CH 3 NH 2 , CH 3 OH, HCl, and HF have been determined in the gas phase at low pressures and room temperature. CH 2 (ã ¹ A 1 ) was generated by pulsed laser photolysis of CH 2 CO. The measurements were carried out by observing the laser induced fluorescence of ¹ CH 2 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 · 10 ¹⁴ cm ³ /mol s, respectively. NH 2 was shown by LIF detection to be a primary product of the reaction of ¹ CH 2 with NH 3 . The intersystem crossing channel of ¹ CH 2 was investigated by monitoring the formation of CH 2 (X̃ ³ B 1 ) with laser magnetic resonance. LMR absorption intensities of ³ CH 2 resulting from quenching of ¹ CH 2 in the presence and absence of the reactant R were compared under otherwise identical conditions. The branching ratios of quenching versus total removal of ¹ CH 2 , turned out to be 0.30, 0.13 and 0.98 for NH 3 , CH 3 OH, and HF, respectively.

The gas phase reactions ¹⁸ OH + H ¹⁶ O 2 → H 2 ¹⁸ O + ¹⁶ O 2 (1a) ¹⁸ OH + H ¹⁶ O 2 → ¹⁶ OH + H ¹⁸ O ¹⁶ O (1b) were studied at room temperature in a discharge flow reactor with far infrared laser magnetic resonance (LMR) detection of ¹⁶ OH, ¹⁸ OH and H ¹⁶ O ¹⁶ O. The formation of ¹⁶ OH in the course of the reaction was observed. The absolute rate constant for the overall removal of ¹⁸ OH in excess of H ¹⁶ O ¹⁶ O was determined. Each run was accompanied by a control experiment replacing the initial ¹⁸ OH by the same amount of ¹⁶ OH. From these experiments a branching ratio is obtained of k 1a /( k 1a + k 1b ) = 0.52 ± 0.08

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 k (4)/√K 2() = (8.53+0.08) · 10-11 cm3/2 s-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.