INORGANIC GAS-PHASE REACTIONS OF THE NITRATE RADICAL - I2+NO3 AND I+NO3

A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine, for the first time, bimolecular rate coefficients for the reactions between I2 and NO3, k1 = (1.5 +/- 0.5) x 10(-12) cm3 molecule-1 s-1, and I and NO3, k2 = (4.5 +/- 1.9) x 10(-10) cm3 molecule-1 s-1. No temperature dependence over the range 292-423 K, or pressure dependence from 1.2 to 4.7 Torr, was observed for the reaction I2 + NO3. A heterogeneous generation of I atoms was observed in the I + NO3 reaction system which was interpreted as evidence for the reaction of IO at the surface of the flow reactor to form a higher oxide of iodine and iodine atoms. The rate coefficient for reaction of IO at the walls to form I was found to be 25-45 s-1. An upper limit for the heat of formation of IONO2 of 21 +/- 3 kJ mol-1 was also derived.