Absorption Spectra of Polyatomic Molecules at High Temperatures. II. Benzene and Perfluorobenzene. Kinetics of the Pyrolysis of Benzene

Abstract

The near-ultraviolet absorption spectra of benzene and of hexafluorobenzene vapors were measured over the range 690° to 1900°K. The samples were diluted with argon (90%—99% of inert gas) and shock heated. Absorption coefficients were evaluated at a fixed frequency (Hg, λ2537) as a function of time after passage of the shock front [Iλ(t)], and as a function of wavelength at a fixed time interval [Iτ(λ)]. For temperatures below 1300°K for C6H6 and 1600°K for C6F6, absorptions were recorded prior to the occurrence of significant decomposition of the sample; above these temperatures values were deduced for benzene from measurements extrapolated to zero time. Integrated absorption coefficients (f) for the 1B2u←1A1g transition were evaluated for the range in temperature given above and were compared with theoretical analyses of the effect of temperature on f numbers. A mechanism for the pyrolysis of benzene is proposed which is compatible with flow experiments through tubes at 1500°K and the present shock-tube data.