A Flowing Afterglow Study of the Reaction C_2+NO →CN (B^2Σ^+, A^2II)+CO

The C_2+NO reaction has been studied by observing the CN (B-X) and CN (A-X) chmiluminescence. Experiments have been performed by using either a conventional flowing afterglow or a low-pressure apparatus. The C_2 radicals have been generated by Ar afterglow reaction of C_2H_2, CH_4, or CO molecule. In the flowing afterglow experiment, very intense perturbed rotational lines of CN (A, v'=10) appear in the CN (B-X) emission spectrum when C_2H_2 is used, while the perturbed rotational lines are relatively weak when CH_4 or CO is employed. Possible excitation sources for creating the CN (B, A) states are C_2 (a) and C_2 (X). On addition of C_6H_6 as a scavenger of C_2 (X), both the spectral features of the CN (B-X, A-X) emissions and the product branching ratio k_ /k_ have not changed in the former spectra, whereas they changed considerably in the latter spectra. These results can be explained by the facts that the CN (B, A) states are excited from the C_2 (a)+NO reaction when C_2H_2 is used, while they are produced from both the C_2 (a)+NO and C_2 (X)+NO reaction when CH_4 and CO are employed. The rovibrational distribution of CN (B) and the vibrational distribution of CN (A) resulting from the C_2 (a)+NO reaction have been determined. These distributions are in agreement with statistical prior ones, suggesting that the CN (B, A) states are formed through long lived complexes.