THERMAL-DECOMPOSITION OF CH3I USING I-ATOM ABSORPTION

The recently developed I-atom atomic resonance absorption spectrometri c (ARAS) technique has been used to study the thermal decomposition ki netics 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 x 10(-9) exp(-19858 WT) cm(3) mol ecule(-1) s(-1). Two unimolecular theoretical approaches were used to rationalize the data. The more extensive method, RRKM analysis, indica tes that the dissociation rates are effectively second-order, i.e., th e magnitude is 61-82% of the low-pressure-limit rate constants over 10 52-1616 K and 102-828 torr. With the known E-0 = Delta H-0(0) = 55.5 k cal mole(-1), the optimized RRKM fit to the ARAS data requires(Delta E )(down) = 590 cm(-1). (C) 1997 John Wiley and Sons, Inc.