Exchange reaction of acetylene-d2 with hydrogen chloride

Abstract

Publication costs assisted by the National Science FoundationA mixture containing 3% each of the reactants CzDz and HC1 in an Ne-Ar diluent was studied over the temperature range 1650-2600 K utilizing a shock tube coupled to a time-of-flight mass spectrometer. Plots of the mole fractions f of the exchange products, DC1 and CzHD, revealed two distinct regions of growth: (a) an initial low conversion region characterized by an induction period ti; and (b) a region of accelerated exchange during which exchange products were formed with a quadratic dependence of the reaction time. These two regions labeled a and b were combined using two empirical equations, 1 -fa/feq,a = exp-[-k,[M]t], where t 5 ti, and 1 -fb/feq,b = exp[-kb[M](t -ti)2], in order to represent the entire reaction profile at any given temperature within the interval investigated. The Arrhenius parameters for k , and k b were determined to be 1011.15*0.30 exp(-19990 f 2850/RT) and 1016.40*0.41 exp(-31480 f 4200/RT), respectively, for DC1 and 1011.69*0.29 exp(-19150 f 2740/RT) and 1015.24*0.34 exp(-17620 f 3480/RT) forCzHD. The units for k , are cm3 mol-l sec-l and cm3 mol-l s e c 2 for kb. Activation energies are reported in cal mol-l. Comparison with the profiles obtained for acetylene pyrolysis strongly suggests that the mechanism for the exchange is atomic. Furthermore, the exchange experiments indicate that the initial step in the pyrolysis of acetylene is the disproportionation reaction, 2C2H2 -CZH + CzH3.