Fluorescence quenching of NCO in CH4/O2 and CH4/air premixed low pressure flames

The fluorescence quenching rate constant for the à state of NCO has been determined for NO doped CH4/O2 and CH4/air premixed flames by directly measuring the fluorescence decay times over the pressure range 10–100 Torr. The rate constant kQP for the NCO Ã2Σ+ (000) state in a stoichiometric CH4/O2 flame with NO is 1.03 ± 0.07 μs−1 Torr−1. The rate constant measured for a similar CH3/air flame (0.54 ± 0.05 μs−1 Torr−1 is smaller by a factor of 2. The ratio of NCO quenching rate constants for CH4/O2 compared to CH4/air flames is similar to those for other species such as NO. A somewhat larger rate constant (1.31 ± 0.08 μs−1 Torr−1) is measured for vibrationally excited levels of the à state of NCO, possibly due to vibrational energy transfer in the excited state.