The recently developed I-atom atomic resonance absorption spectrometric (ARAS) technique has been used to study the thermal decomposition kinetics of CH 3 I over the temperature range, 1052 -1820 K. Measured rate constants for CH 3 I between 1052 and 1616 K are best expressed by k . 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 , the optimized RRKM fit to the ARAS data requires .