The Hydrocarbon-induced Fluorescence of Atoms in Flames

Abstract

The phenomenon of chemiluminescent emission from atoms introduced into hydrocarbon flames has been studied in a basic hydrogen-oxygen diffusion flame at low hydrocarbon concentrations. Emissions from several atoms are first order in methane concentration and examination of the relative populations of the excited states of arsenic suggests a single excitation mechanism with available energy in excess of 8.5 eV. Previously proposed mechanisms are discussed and the available evidence favors the process C H + O + C H O as the origin of the energy of excitation.Le phenomene de 1'6mission par chimioluminescence a partir d'atomes introduits dans une flamme d'hydrocarbure a Bte Btudie dans une flamme de diffusion hydrogene-oxygene a faible concentration en hydrocarbure. Les emissions de diffkrents atomes sont du premier ordre par rapport a la concentration en methane et I'examen des populations relatives dans les etats excites de l'arsenic, suggere un mecanisme d'excitation unique avec un exces d'knergie disponible de 8.5 eV. On discute des mecanismes proposes anterieurement ainsi que de la preuve qui existe en faveur du processus: Canadian Journal of Chemistry, 49. 2476 (1971)Atomic emissions may be observed from both the primary reaction zone and the outer combustion zone of hydrocarbon-oxygen flames seeded with com~ounds of some of the elements. In the outer zone the emission arises from atoms previously excited either thermally or by the reactions (1) H + H + M + M * + H z and H + O H + M -+ M * + H Z O the energy limit of excitation being determined by the exothermicity of the latter process, 5.2 eV. The spectrum observed in the primary reaction zone is commonly more extensive, including emissions from much higher energy levels, the extreme case being a zinc level at 9.0 eV (2). Since these emissions arise from the region of the flame defined by the blue and green emissions from C H and C,, it may be assumed that the energy for the atomic excitation arises in the oxidation of these, or similar, hydrocarbon species. Thus, while the excitation of the atoms is ~robablv of little preference exists for any one process. We have recently found that it is possible to observe chemiionization and C H emission when low concentrations of hydrocarbons are present in a hydrogenin-oxygen diffusion flame on a commercial flame spectrophotometry burner. This same technique has now been applied to a study of the atomic emissions which arise when volatile inorganic compounds are added to the system. ExperimentalThe apparatus consisted of a Beckman DU-2 spectrophotometer wherein the IP 28 photomultiplier was replaced by an RCA 7200 to facilitate measurements at short wavelength. The burner mount of the flame emission attachment was replaced with a Teflon holder and a spiral electrode was mounted above the primary reaction zone of the flame for rate of ion formation determination. The burner was modified by removing the axial aspirator capillary. Hydrogen (I l/min) containing the gaseous additive and the hydrocarbon entered through the ...

Ion formation in hydrocarbon flames

“…The 'high' level of ion formation from C2H2 might have arisen from an alternate mechanism of conversion of C2H2 to CH, such as postulated in the oxidation studies of Williamson and Bayes (9). To explore this possibility, Klemm and Blades (6) examined two other consequences of hydrocarbon oxidation in a Hz-in-O2 diffusion flame which are first order in CH4 and other hydrocarbon concentrations, and which may depend on the CH concentration, namely CH emission and the hydrocarbon-stimulated emission of As atoms (10,11). Both these additional parameters indicated low responses for C2H2 compared to CH4, C2H6, and C2H4, and Klemm and Blades (6) postulated that the excess ion formation from C2H2 arises from Peeters et al (12) have made rate of ion formation and CH emission measurements on a Hz-O2 premixed flame containing traces of several hydrocarbons and also observe a first order component of CH emission for several hydrocarbons, including CH4.…”