Emission of Vacuum Ultraviolet Radiation from the Acetylenehyphen;Oxygen and the Methanehyphen;Oxygen Reactions in Shock Waves

摘要

The C2H2sngbnd;O2and CH4sngbnd;O2reactions were studied by observing the emission of vacuum ultraviolet radiation from shock waves in gas mixtures containing 85 to 99 Ar and with 2times;10minus;6le;O2le;60times;10minus;6moles/l. In both reactions after an induction period of lengthti,the emission intensity rises exponentially with a time constant tgr; and then decreases about as rapidly. For the C2H2sngbnd;O2reaction, emission predominantly in the wavelength range 1500lgr;1700 A was observed. It was estimated that one photon was emitted in this range per 3times;104C2H2molecules passing through the reaction zone at 1840deg;K. The integrated emission intensity depends on the temperature as if the process producing it has an activation energy of 15 kcal/mole. In the range of conditions 0.65le;O2/C2H2le;3.6 and 1300le;Tle;2200deg;K it was found thatlog10lpar;lsqb;O2rsqb;tirpar;thinsp;thinsp;lpar;molethinsp;thinsp;secsol;lrpar;equals;minus;10.57plus;17thinsp;100sol;4.58T. The data for tgr; from mixtures with 0.65le;O2/C2H2le;7.7 fit the expressionlog10lpar;lsqb;O2rsqb;tgr;rpar;thinsp;thinsp;lpar;molethinsp;thinsp;secsol;lrpar;equals;minus;11.48plus;17thinsp;100sol;4.58Twith a standard deviation of a factor of 1.4 in tgr;. In the first approximation the values of O2tiand O2tgr; are functions of temperature only. In lean mixtures, however, O2tgr; and especially O2tiare larger than the average. These results are explained in terms of a branching chain mechanism in which the reaction H+O2=OH+O plays the dominant role in controlling the rate.The CH4sngbnd;O2reaction was studied in the range of conditions 0.5le;O2/CH4le;4.5 and 1800le;Tle;2700deg;K. The emission intensities are an order of magnitude smaller and more strongly temperature dependent, tgr; is a factor of 2 or 3 larger, andtiis a factor of 20 larger at the low temperatures and a factor of 4 larger at the high temperatures than for the C2H2sngbnd;O2reaction. The kinetic implications of these findings are discussed.