Atomndash;Molecule Kinetics Using ESR Detection. V. Results for Oplus;OCS, Oplus;CS2, Oplus;NO2, and Hplus;C2H4

摘要

The widehyphen;temperaturehyphen;range, fasthyphen;flow reactor with ESR detection used in previous papers of this series has been further improved so that rate coefficients of nearly 1013cm3moleminus;1middot;secminus;1can now be measured by the pseudohyphen;firsthyphen;order method. Results have been obtained over the temperature range 273deg;ndash;808deg;K for the reactionOplus;OCSrarr;COplus;SO,over 227deg;ndash;538deg;K forOplus;CS2rarr;CSplus;SO,and over 297deg;ndash;543deg;K forOplus;NO2rarr;NOplus;O2In Arrhenius form the rate coefficients are (cm3moleminus;1middot;secminus;1)k1thinsp;equals;thinsp;1.9thinsp;times;thinsp;1013explpar;minus;thinsp;4530thinsp;sol;thinsp;RTrpar;; k2thinsp;equals;thinsp;1.2thinsp;times;thinsp;1013explpar;minus;thinsp;1050thinsp;sol;thinsp;RTrpar;; k3thinsp;equals;thinsp;1.0thinsp;times;thinsp;1013explpar;minus;thinsp;580thinsp;sol;thinsp;RTrpar;.The product SO in 1 and 2 was measured in its3Sgr;ground state, and excited vibrational states could not be detected by ESR under our experimental conditions, although the SO must have been so excited initially. Stoichiometry and mechanisms are discussed. The Hthinsp;plus;thinsp;C2H4reaction was also measured in roomhyphen;temperature helium and argon, and in helium at 525deg;K. The data were obtained over a pressure range of about 0.5ndash;2.5 mm, and the pressure dependence of the net rate coefficientktfor Hhyphen;atom decay was clearly measurable. Mass spectrometer analysis showed essentially all of the C2H4to be converted to C2H6and CH4. The mechanism is discussed. From thePminus;1thinsp;equals;thinsp;0intercept of plots ofktminus;1vsPminus;1, the data were assumed to yield values of the rate coefficientk4for the initial step Hthinsp;plus;thinsp;C2H4rarr;C2H5*, i.e., the production of vibrationally excited C2H5* in the Rabinovitch manner. At room temperature the helium data givek4thinsp;equals;thinsp;2.2thinsp;times;thinsp;1011and the argon data1.4thinsp;times;thinsp;1011cm3moleminus;1middot;secminus;1. From the slopes of the two plots the probability for transfer of vibrational energy from C2H5* to translation of argon is found to be about five times greater than for helium. The limited highhyphen;temperature data imply very little temperature dependence for eitherk4or its reverse.