Comparison of the cross-sections and thermal rate constants for the reactions of C(3PJ) atoms with O2 and NO

Abstract

We report the results of two sets of experiments on each of the reactions and

In low temperature (15–295 K) kinetic experiments performed in a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus, the rate constants for these two reactions were found to fit the following expressions:

and

In crossed beam experiments, relative cross-sections for products of the two reactions [CO from (1) and CN from (2a)] in specific vibrational levels were measured at collision energies (ε_tr) between ca. 4 and 100 meV. The cross-sections are proportional to (ε_tr)^−0.94 for reaction (1) and to (ε_tr)^−0.72 for reaction (2a). Both sets of results demonstrate that these reactions proceed over potential energy surfaces with no barrier on the path from reactants to products. If the reaction cross-sections are independent of the rotational energy level of the reagents and of the distribution of C(³P_J) atoms over spin–orbit states, and if they exhibit the same dependence on relative translational energy below 4 meV as above, integration of the excitation functions leads to the rate constants exhibiting temperature dependences of k₁(T) proportional to T^−0.44 and k_2a(T) proportional to T^−0.22, in reasonable agreement with the direct measurements of the rate constants for reactions (1) and (2). The two sets of experimental results are also compared with theoretical calculations, based on the adiabatic capture centrifugal sudden approximation (ACCSA) model. The calculations correctly predict the temperature dependence of the rate constants for both reactions. The consistency of these three data sets is discussed.