Unimolecular Decomposition of t-C4H9 Radical

Abstract

The kinetics of the unimolecular decomposition of the t-C[sub 4]H[sub 9] radical has been studied. The reaction was isolated for quantitative study in a heated tubular flow reactor coupled to a photoionization mass spectrometer. Rate constants for the decomposition were determined in time-resolved experiments as a function of temperature (712-779 K) and bath gas density ((3-22) x 10[sup 16] molecules cm[sup [minus]3]) in He. The rate constants are in the falloff region under the conditions of the experiments. A transition-state model was created to obtain values of the microcanonical rate constants, k(E), needed to solve the master equation. The transition-state model provides the high-pressure limit rate constants for the decomposition reaction (k[sub 1][sup [minus]](t-C[sub 4]H[sub 9] [yields] i-C[sub 4]H[sub 8] + H) = 2.18 x 10[sup 9]T[sup 1.48] exp(-18120 K/T) s[sup [minus]1]) and the reverse reaction (k[sub [minus]1][sup [infinity]](H + i-C[sub 4]H[sub 8] [yields] t-C[sub 4]H[sub 9]) = 1.03 x 10[sup [minus]11] T[sup 0.25] exp(-737 K/T) cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]). The results of earlier studies of reactions of decomposition of t-C[sub 4]H[sub 9] and the reverse reaction which reported the value of the enthalpy of formation of t-C[sub 4]H[sub 9] were reanalyzed, and the resultant value of [Delta]H[submore » f][degrees][sub 298](t-C[sub 4]H[sub 9]) is in agreement with the most current measurements. 51 refs., 8 figs., 3 tabs.« less