Photochemical Effects in Two-Photon-Excited Fluorescence Detection of Atomic Oxygen in Flames

Abstract

Much of the recent attention on developing techniques for measuring radical concentrations in flames, and atoms in particular, has focused on the use of multiphoton excitation schemes. One of the early papers on atomic oxygen detection in flames reported photochemical production of oxygen atoms in room air,1 drawing attention to the need for caution to make sure that these optical techniques are in fact as nonintrusive as they are claimed to be. We demonstrated recently that photochemical effects can have a strong influence in 205-nm, two-photon-excited fluorescence detection of atomic hydrogen in atmospheric-pressure flames.2 In this paper we report similar effects in measuring atomic oxygen concentration in flames, and demonstrate that excess atomic oxygen concentrations can be produced by single-photon excitation of the Schumann-Runge bands of vibrationally excited oxygen molecules present in the flame.