Thermal decomposition of CH3I using I-atom absorption

The recently developed I-atom atomic resonance absorption spectrometric (ARAS) technique has been used to study the thermal decomposition kinetics of CH₃I over the temperature range, 1052–1820 K. Measured rate constants for CH₃I(+Kr)→CH₃+I(+Kr) between 1052 and 1616 K are best expressed by k(±36%)=4.36×10^?9 exp(?19858 K/T) cm³ molecule^?1 s^?1. Two unimolecular theoretical approaches were used to rationalize the data. The more extensive method, RRKM analysis, indicates that the dissociation rates are effectively second-order, i.e., the magnitude is 61–82% of the low-pressure-limit rate constants over 1052–1616 K and 102–828 torr. With the known E₀=ΔH₀⁰=55.5 kcal mole ^?1, the optimized RRKM fit to the ARAS data requires (ΔE)_down=590 cm^?1. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 535–543, 1997.