Absolute concentrations of the C2 radical in the A 1Πu state measured by cavity ring down spectroscopy in an atmospheric oxyacetylene flame

Measurements of absolute concentrations of C-2 (A (1)Pi(u)) in an atmospheric oxyacetylene flame are presented. Cavity ring down spectroscopy (CRDS) was applied to measure lateral column density profiles at a number of vertical positions. By means of Abel inversion processing and estimated radial temperature profiles, the column densities were converted to absolute concentration profiles, which have central maxima with peak concentrations between 8x10(14) and 2.5x10(15) m(-3). Comparison of the measured A state concentration profiles with calculated ground state C-2 profiles supports an earlier suggestion that the gas-phase mechanism used in the calculations needs improvement. This work demonstrates the applicability of CRDS for measuring absolute concentrations of electronically excited species in atmospheric flames, a result which can be of importance to combustion research. (C) 2002 American Institute of Physics.