Kinetic and thermodynamic properties of INO and INO2 intermediate complexes in iodine recombination

The recombination of iodine atoms after laser flash photolysis has been studied in the presence of NO or NO2 at 320–450 K and 0–200 atm of He. The reaction proceeds in two stages. The first stage is governed by the recombination I+NO(+He) →INO(+He) or I+NO2(+He) →INO2(+He), for which the full falloff curves are derived. The second stage is governed either by reaction between two INO (or INO2) molecules, or, at higher temperatures, by thermal decomposition of INO (or INO2). The reaction involves the elementary steps of a typical intermediate complex mechanism of atom recombination. The rates of all of these elementary steps can be separated. From the I+NO⇄INO and I+NO2⇄INO2 equilibrium constants the enthalpies of formation of INO and INO2 of ΔHfo298(INO) =29.0±1 kcal mol−1 and ΔHfo298(INO2) =14.4±1 kcal mol−1, respectively, are derived.