ENERGY-TRANSFER IN THE A(2)SIGMA(-PRESSURE CH4() STATE OF OH FOLLOWING UPSILON'=1 EXCITATION IN A LOW)O-2-FLAME/

Using temporally, spectrally and spatially resolved laser induced fluo rescence (LIF), collision-induced energy transfer was studied in the A (2) Sigma(+)(upsilon' = 1) level of OH. Measurements were performed in a laminar premixed flame at 10 Torr total pressure. The low pressure allowed the spatial variation of the effective quenching rate to be de termined through the flame front. In addition, the dependence of the q uenching rate on rotational quantum number was measured by exciting a series of rotational lines in the range N' = 0-16. The results show th at the total quenching rate decreases only 17% through the flame front , in the region where OH can be detected. Nevertheless, the absolute v alue of the quenching rate Q is required if absolute concentrations ar e to be determined from LIF-signals. The variation both of Q and of th e rotational relaxation rate with excited rotational quantum state mus t be known for quantification of LIF-temperature measurements via the Boltzmann relation. Finally, the rotational and vibrational energy tra nsfer (RET, VET), was investigated by recording the spectrally and tem porally resolved fluorescence. For all excited rotational lines, effic ient RET to neighbouring rotational states was observed, but only very little VET. Total RET rates were determined from the difference betwe en the time-resolved broadband (total fluorescence) and narrowband (fl uorescence from the laser excited level) curves. The experimental resu lts were compared with simulations using a dynamic model, which descri bes the energy transfer for flame conditions. With the available input data (temperature, major species concentrations and collision-partner specific RET cross sections), good agree ment was obtained.