, Volume 79, Issue 1, pp 113-120
Date: 31 Mar 2004

Study of energy transfer processes in CH as prerequisite for quantitative minor species concentration measurements

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Abstract

Energy transfer effects on CH A-X (0,0) laser-induced fluorescence spectra have been studied for the first time in rich methane and acetylene atmospheric-pressure flames using a picosecond laser system in conjunction with a streak camera. Results allowed determination of typical fluorescence lifetimes of levels in the A state populated by rotational energy transfer (RET), and of state-dependent quenching. These values are used to extend the LASKIN simulation program that has originally been developed to study energy transfer processes in OH, for modelling of spectra of the CH A-X (0,0) transition. Results show good agreement between experiment and simulation both in the spectrally as well as in the temporally-resolved regime.

Additionally, a novel strategy for quantitative CH measurements relying on time-resolved broadband detection after excitation in the A-X (0,0) band is presented . This method allows determination of both the fluorescence lifetime and the quench-free amplitude of the fluorescence, which is directly proportional to the CH number density. Results obtained in acetylene flames show significantly higher quenching than expected from extrapolations using published coefficients. This discrepancy is most likely due to an incorrect value for the quenching of CH by collisions with CO.

PACS

06.60.Jn; 33.50.-j; 34.50.Ez