Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part II: reactions with alkenes (ethylene, propene, 1-butene), dienes (allene, 1,3-butadiene) and alkynes (acetylene, propyne and 1-butyne)

Abstract

The kinetics of the reactions of the linear butadiynyl radical, C₄H (CCCCH), with a variety of unsaturated hydrocarbons have been studied over the temperature range of 39–300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or reaction kinetics in uniform supersonic flow) apparatus combined with the pulsed laser photolysis–laser induced fluorescence technique. The rate coefficients for all the reactions studied are found to all be in excess of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ over the entire temperature range. They can be fitted with the following expressions (valid from 39 K to 300 K, with RMS deviations of the experimental points from the predicted values shown, to which should be added 10% possible systematic error) for reaction of C₄H with alkenes: k_C2H4 = (1.95 ± 0.17) × 10⁻¹⁰ (T/298 K)^−0.40 exp(9.4 K/T) cm³ molecule⁻¹ s⁻¹;k_C3H6 = (3.25 ± 0.12) × 10⁻¹⁰ (T/298 K)^−0.84 exp(−48.9 K/T) cm³ molecule⁻¹ s⁻¹;k_1-C4H8 = (6.30 ± 0.35) × 10⁻¹⁰ (T/298 K)^−0.61 exp(−65.0 K/T) cm³ molecule⁻¹ s⁻¹,for reaction of C₄H with dienes:k_C3H4 = (3.70 ± 0.34) × 10⁻¹⁰ (T/298 K)^−1.18 exp(−91.1 K/T) cm³ molecule⁻¹ s⁻¹;k_1,3-C4H6 = (5.37 ± 0.30) × 10⁻¹⁰ (T/298 K)^−1.25 exp(−116.8 K/T) cm³ molecule⁻¹ s⁻¹,and for reaction of C₄H with alkynes: k_C2H2 = (1.82 ± 0.19) × 10⁻¹⁰ (T/298 K)^−1.06 exp(−65.9 K/T) cm³ molecule⁻¹ s⁻¹;k_C3H4 = (3.20 ± 0.08) × 10⁻¹⁰ (T/298 K)^−0.82 exp(−47.5 K/T) cm³ molecule⁻¹ s⁻¹;k_1-C4H6 = (3.48 ± 0.14) × 10⁻¹⁰ (T/298 K)^−0.65 exp(−58.4 K/T) cm³ molecule⁻¹ s⁻¹.Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and star-forming regions, are considered.