The reaction of hydrogen atoms with chlorine has been studied in a discharge-flow system using electron spin resonance detection of H-atoms. Chlorine consumption and hydrogen chloride production, measured by on-line mass spectrometry, were much lower than expected. This is explained by the enhanced rate of the reaction H + HC1+ H2 + C1 due to vibrational excitation of the HCl produced in the initial step. Based on a mechanism including this enhanced reaction rate an Arrhenius relation, (4.6k 1.3) x 1Olo exp[-(5 9404 840) J mol-l/RT] dm3 mol-' s-l, is obtained for the rate constant of the initial step over the temperature range 292-434 K.The reaction between hydrogen atoms and chlorine is an important reaction in the H,+C12 system.l Comprehensive studies have been made by Polanyi and co-workers on the energy distribution of the reaction products. Surprisingly few measurements have been made of the absolute rate constant of the r e a ~t i o n . ~ An Arrhenius equation k = 3.7 x loll exp[ -(7 500+ 1 300) J mol-l/RT] dm3 mol-l s-l was obtained by a mass spectrometric method under conditions of high H/C12 ratio. A discharge-flow, time of flight mass spectrometric measurement yielded a value of k = 2.1 x lofo dm3 mol-1 s-l, again in the presence of excess H-atoms.It is desirable to obtain independent confirmation of the Arrhenius parameters for the rate constant using the present e.s.r. reaction system because of the potential importance of the rate of the H + CI2 reaction in a series of chlorine atom abstraction systems under investigation in this laboratory.
The reaction of hydrogen atoms with hydrogen chloride has been studied in a discharge-flow system using electron spin resonance detection of H-atoms and mass spectrometric analysis. The Arrhenius relation log (kl/dm3 mol-1 s-') = (9.6720.10)-[(13 3002700)J mol-'/2.303 RT] was obtained for the rate constant of the initial step
The reactions of hydrogen and oxygen atoms with acetone have been studied in a dischargeflow system using electron spin resonance detection of atoms, together with mass spectrometric and gas chromatographic analyses of stable species. The Arrhenius relations obtained for the initial reaction steps were lOg(kH atom/dm3 mol-' s-') = (10.27kO.20)-"(26 600k 1 200) J m01-'/2.303 RT] for 298-465 K and log(k0 atom/dm3 mol-' s-') = (9.63 kO.10)-[(23 800rt700) J mol-'/2.303 RT] for 298-621 K.Very few studies have been made of the reactions of atoms with oxygen-containing molecUles.l~ Kinetic data on these systems are of importance in leading to an understanding of oxidation processes and for comparison with the more extensive data available on reactions of hydrocarbons with these species. The reaction of oxygen atoms with acetone has not been studied previously while the reaction of hydrogen atoms with acetone has been investigated only at room t e r n p e r a t ~r e . ~ EXPERIMENTAL with the addition of a gaschromatography sampling facility for gases condensable at 77 K, by bleeding a sample of the gas flow through a removable trap downstream of the e.s.r. cavity. The chromatographic analysis employed Porapak N and Porapak S columns, with flame ionisation and katharometer detection, and blank analyses with the atom supply off were performed to compensate for traces ( t 0 . 1 %) of water and acetic acid present as impurities in the acetone. The mass
Die Kinetik der Titelreaktion wird in einem Entladungs‐Strömungs‐System mit Hilfe von ESR (Nachweis von H‐Atomen) und massenspektrometrischer Analyse im Temperaturbereich von 298‐521 K untersucht.
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