Energy transfer in combustion diagnostics: Experiment and modeling

Laser induced fluorescence (LIF) of OH (A (2)Sigma (+)) is measured in seve ral atmospheric-pressure flames using a short-pulse laser system (80 ps dur ation) in conjunction with an intensified streak camera. The two-dimensiona l signal-detection technique allows one to simultaneously monitor rotationa l and vibrational relaxation as well as electronic quenching. Rotationally- resolved LIF spectra affected by energy transfer are compared with the resu lts of a rate-equation model and are found to be in reasonably good agreeme nt. It is shown that a significant contribution of fluorescence detected by broad-band techniques is due to levels populated by vibrational energy tra nsfer (VET). Implications for picosecond LIF techniques for the time-resolv ed, quench-free detection of OH are discussed. A detailed analysis is prese nted for fluorescence spectra originating from levels populated by VET afte r excitation of states in the OH (A (2)Sigma (+), v' = 2) level.