Temperature Dependence of C₂(<em>X</em>¹<em>&Sigma;</em>_g⁺) in Reactions with Unsaturated Hydrocarbons

Abstract

Bimolecular rate constants for the gas-phase reactions of C2(X 1 Σ + g) with unsaturated hydrocarbons C2H4 and C2H2 were measured over the temperature range 293-573 K by pulsed laser photolysis/laserinduced fluorescence (PLP-LIF). The rate constants, in the unit of cm 3 •molecule-1 •s-1 , can be fitted by the normal Arrhenius expressions: k(C2H4)=(1.16±0.10)×10-10 exp[(290.68±9.72)/T], and k(C2H2)=(1.36±0.02)× 10-10 exp[(263.85 ± 7.60)/T], where all error estimates are ± 2σ and represent the precision of the fit. The observed bimolecular rate constants along with the negative temperature dependences of k(T) allow us to conclude that the reactions of C2(X 1 Σ + g) with these unsaturated hydrocarbons in the temperature range 293-573 K proceed via an addition mechanism.