The I-atom atomic resonance absorption spectrometric (ARAS) technique has been used in Kr bath gas to study the thermal decomposition kinetics of iodobenzene, C 6 H 5 I, over T- and P-ranges of 1082-1416 K and 103-731 Torr, giving the first order expression, k(± 60%) = 1.982 10 1 1 exp(- 23120 K/T) s - 1 . Two unimolecular theoretical approaches were used to rationalize the data implying E 0 = Δ H 0 0 = (66.7 ± 0.7) kcal mol - 1 and Δ E d o w n = (447 ± 92) cm - 1 .