Kinetics and thermodynamics of the CN molecule. III. Shock tube measurement of CN dissociation rates

Abstract

The dissociation of CN molecules in an argon diluent has been investigated in a shock tube over the temperature range 4400 to 13 000 °K. Observations of CN(B 2Σ+→X 2Σ+) and C2(d 3Πg→a 3Πu)d emission support the following chain as a sufficient decomposition mechanism: CN+M=C+N+M (1); C+CN=C2+N (2); N+CN=N2+C (3); C2+M=2C+M (4); N2+M=2N+M (5); and rate coefficients have been measured for the first four reactions. The measured rate coefficients for reaction (1) were in good agreement with an earlier measurement by Fairbairn and with a theoretical modified phase space estimate by Shui. An initial induction period was identified prior to steady state dissociation, and excess molecular nitrogen was observed to significantly inhibit the CN decomposition chain. Experimental CN and C2 emission records both from the present investigation and from earlier work by Fairbairn and by Patterson and Greene are compared with predicted excited state concentrations obtained by numerical integration of the rate equations. The results of earlier investigations are reinterpreted as limiting cases of the proposed decomposition chain.