Spectroscopic investigation of acetylene-nitrous oxide flames

Abstract

An extended systematic spectroscopic investigation of C 2 H 2 +N 2 O flames burning at low pressure has been carried out for the free radicals CH (X 2 Π and A 2 Δ), OH (X 2 Π and A 2 Σ + ), CN (X 2 Σ + , A 2 Π i and B 2 Σ + ), NH (X 3 Σ − and A 3 Π i ) and C 2 ( a 3 Π u and d 3 Π g ). The results can be summarized as follows: o -All the excited radicals are produced mainly via chemiluminescent reactions. The CN (A 2 Π i ) concentration is of the same order of magnitude as the ground state concentrations of CN (X 2 Σ + ) or NH (X 3 Σ − ). -The reaction of nitric oxide with CH radicals plays a key role and leads to the formation of mainly CN (A 2 Π i ) or NH (X 3 Σ − ). -The CN (B 2 Σ + ) formation is attributed to the reaction r-4 C 2 ( a 3 Π u )+NO→CN (B 2 Σ + )+CO -The reaction r-8d CN (A 2 Π i )+OH→NH (A 3 Π i )+CO could account for the formation of the NH (A 3 Π i ) with a rate constant of about (8±2) 10 −12 cm 3 molecule −1 s −1 . -The OH (A 2 Σ + ) formation may result from the reaction r-11 NH+NO→N 2 +OH (A 2 Σ + ) accounting for the low rotational temperature of OH (A 2 Σ + ) observed in C 2 H 2 +N 2 O flames. -The processes r-2 C 2 ( a 3 Π u )+OH→CH (A 2 Δ)+CO and r-3 CH 2 (CH)+C→C 2 ( d 3 Π g )+H 2 (H) are in good agreement with the behaviour of C 2 ( d 3 Π g ) and CH (A 2 Δ) in C 2 H 2 +N 2 O flames.