The thermal decomposition of cyanogen azide (NCN 3 ) and the subsequent collision-induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state 1 NCN and ground state 3 NCN radicals. NCN was generated by the pyrolysis of NCN 3 behind shock waves and by the photolysis of NCN 3 at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN 3 in argon have been extracted from 1 NCN concentrationtime profiles in the temperature range 617 K < T < 927 K and at two different total densities: k(ρ ≈ 3 × 10 −6 mol/cm 3 )/s −1 = 4.9 × 10 9 × exp (−71 ± 14 kJ mol −1 /RT ) (±30%); k(ρ ≈ 6 × 10 −6 mol/cm 3 )/s −1 = 7.5 × 10 9 × exp (−71 ± 14 kJ mol −1 /RT ) (±30%). In addition, high-temperature 1 NCN absorption cross sections have been determined in the temperature range 618 K < T < 1231 K and can be expressed by σ/(cm 2 /mol) = 1.0 × 10 8 − 6.3 × 10 4 K −1 × T (±50%). Rate constants for the CIISC process have been measured by monitoring 3 NCN in the temperature range 701 K < T < 1256 K resulting in k CIISC (ρ ≈ 1.8 × 10 −6 mol/cm 3 )/s −1 = 2.6 × 10 6 × exp (−36 ± 10 kJ mol −1 /RT ) (±20%), k CIISC (ρ ≈ 3.5 × 10 −6 mol/cm 3 )/s −1 = 2.0 × 10 6 × exp (−31 ± 10 kJ mol −1 /RT ) (±20%), k CIISC (ρ ≈ 7.0 × 10 −6 mol/cm 3 )/s −1 = 1.4 × 10 6 × exp (−25 ± 10 kJ mol −1 /RT ) (±20%). These values are in good agreement with CIISC rate constants extracted from corresponding 1 NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. C 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: [30][31][32][33][34][35][36][37][38][39][40] 2013