Kinetics of Gas-Phase CN by Diode Laser Absorption

Article abstract of DOI:10.1021/j100285a019

Absolute rate constants for the reaction of CN with H2, D2, and CH4 are reported by using a diode laser to probe CN disappearance and HCN growth.The reactions were studied at room temperature over the pressure range 1-200 Torr.The following rate constants were obtained by monitoring the decay of CN (X²Σ⁺) on the P(7) (ν' = 1 <- ν'' = 0) transition at 2015.22 cm^-1: k(CN+H2) = (2.6 +/- 0.3) x 1E-14, k(CN+D2) = (7.2 +/- 0.9) x 1E-15, and k(CN+CH4) = (7.8 +/- 0.9) x 1E-13 cm³ s^-1, where the uncertainties represent +/-2?.The growth of HCN was monitored on the (0,0,1) <- (0,0,0) P(10) transition at 3280.987 cm^-1 at total pressures of 5-100 Torr.We obtained the rate constant k(CN+H2) = (2.2 +/- 0.9) x 1E-14 cm³ s^-1, where the uncertainty represents +/-2?.Transition-state-theory calculations based on ab initio potential energy surface were used to determine the kinetic isotope effect for the reaction of CN with H2 and D2.The predicted value of k(H2)/k(D2) = 3.55 is in excellent agreement with our experimental ratio of 3.6.The integrated line strength for the P(7) (ν' = 1 <- ν'' = 0) transition of CN (X²Σ⁺) was measured under low-pressure conditions where only natural and Doppler broadenings contribute to the half-width.The measured value, assuming Φ_CN = 2 in the 193-nm photolysis of C2N2, is (2.0 +/- 0.8) x 1E-19 cm² molecule^-1 cm^-1, where the uncertainty represents +/-1?.