Temperature dependence of the CN radical reactions with C ₂ H ₂ and C ₂ H ₄

The temperature dependence of the reaction rates for CN radicals with C ₂ H ₄ and C ₂ H ₄ and C ₂ H ₂ has been measured from room temperature to 700 K. The two laser photoionization/LIF-probe technique was used by photolyzing ICN at 266 nm and monitoring CN depletion via B ↔ X LIF at 388 nm. A resistively heated slow-flow gas reactor was employed at 50 Torr total pressure for the temperature dependence study. Both reactions were found to have rate constants that decreased with temperature, fitting k _{C 2 H 4} = (4.72±0.25)×10 ^-11 exp[(509±20)/T] and k _{C 2 H 2} = (3.49±10 ^-11 exp[(571±23)/T] cm ³ molecule ^-1 s ^-1 , indicating that both reactions occur by addition-elimination mechanism. No pressure dependence was observed within experimental errors.