OPTICAL ABSORPTION MEASUREMENTS OF GROUND-STATE CN IN ACTIVE NITROGEN FLAMES

Concentrations of CN in the X 2∑, v=0 level as low as 1×10-9 molecules cm-8 have been detected in active nitrogen flames at pressures from 0.5 to 20 torr by optical absorption spectroscopy using a CN discharge light source and a refined ac detection method. A systematic study of CN B 2∑+↔X 2∑+ absorption and emission intensity as a function of pressure and fuel has provided additional information about the mechanisms of formation and removal of ground-state CN in these systems. An estimate of 3×10-14 cm3 molecule-1·sec -1 for the rate constant for removal of X2∑ CN by H2 has been obtained by determining the effect of added gases on steady-state concentrations. High-resolution measurements have revealed that the rotational population distribution in the ground vibrational level is thermal at pressures as low as 0.5 torr; this result is consistent with the estimated lifetime of ground-state CN in active nitrogen flames.