Laser Flash Photolysis Study of the Br + i-C4H10 HBr + t-C4H9 Reaction. Heat of Formation of t-C4H9

Article abstract of DOI:10.1021/j100177a048

The heat of formation of the tert-butyl radical has been determined in two independent ways using laser flash photolysis coupled with detection of Br by resonance fluorescence.The t-C4H9 + HBr reaction was studied by monitoring the rise of the Br product at room temperature following photolysis of (t-C4H9)2N2 at 351 nm.Combination of the rate constant with k(Br+i-C4H10) gives ΔH^<*>_f,298(t-C4H9) = 50.9 +/- 3.5 kJ mol^-1.The measured value of k(t-C4H9+HBr) ((3.2 +/- 1.0) x 10^-11 cm³ molecule^-1 s^-1) is in reasonable agreement with the measurements of Russell et al. and of Richards et al.Equilibration in the reaction system Br + i-C4H10 <*> HBr + t-C4H9 was studied by generating Br by photolysis of CF2Br2 at 248 nm in the presence of i-C4H10 and HBr and observing the relaxation of
.These experiments were conducted at 573 and 641 K.The measurements yield data for both forward and reverse rate constants, for the equilibrium constant, and hence for ΔH^<*>_f,298(t-C4H9), giving values of 44.2 +/- 4.0 and 48.1 +/- 4.0 kJ mol^-1 at the respective temperatures.Combination of the three independent estimates gives ΔH^<*>_f,298(t-C4H9) = 47.3 +/- 3.5 kJ mol^-1.The values for k(t-C4H9+HBr) at these elevated temperatures agree with the data of Russell et al. and demonstrate a negative temperature dependence in the rate constant.