Falloff Curve and Secific Rate Constants for the Reaction NO2+NO2N2O4

Article abstract of DOI:10.1021/j100326a027

The rate of association of NO2 to N2O4 was measured in N2 at pressures from 1 to 207 bar.This way the reaction was observed in a large section of its falloff range.The relaxation of NO2/N2O4 mixtures was followed after laser flash photolysis of N2O4 at 248 nm.From the results the falloff curve was constructed, which gives the high- and low-pressure rate constants at 298 K (in cm³ molecule^-1 s^-1): k_ass^infinite=(8.3+/-1.0)*10^-13 and k_ass⁰=(1.4+/-0.2)*10^-33.Earlier measurements, believed to be in the low-pressure regime, have not been free from falloff effects.The low value of k^infinite was analyzed with the statistic adiabatic chanell model, and specific rate constants, k(E,J), were calculated.They increase very steeply with energy just above the reaction treshold and go through maxima at low excess energies.These unusual effects are analyzed theoretically and the strong contributions are pointed out of the low-frequency vibrations which disappear during the dissociation of N2O4.