DETERMINATION OF METHYL RADICAL CONCENTRATIONS IN A METHANE AIR FLAMEBY INFRARED CAVITY RINGDOWN LASER-ABSORPTION SPECTROSCOPY

Infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) is e mployed to determine absolute methyl radical concentrations in a 37.5 Torr laminar methane/air flame. IR-CRLAS rovibrational absorption spec tra of the v(3) fundamental band system near 3200 cm(-1) are combined with N-2-CARS temperature measurements to obtain methyl radical concen trations as a function of height above the burner surface. These data are compared with flame chemistry simulations under both stoichiometri c and rich flame conditions. Issues regarding the applicability of IR- CRLAS for combustion studies are discussed, including the uncertaintie s present for the specific case of methyl radical. These IR-CRLAS meas urements indicate the ability to monitor reactants, intermediates, and products within a narrow spectral window, and, to our knowledge, cons titute the first infrared detection of a polyatomic radical in a flame . (C) 1997 American Institute of Physics.