FOURIER-TRANSFORM IR SPECTROSCOPIC OBSERVATION OF GASEOUS NITROSYL IODINE, NITRYL IODINE, AND IODINE NITRATE

Using the photolysis of I2-NOx-N2, mixtures the nitrogen oxyiodines nitrosyl iodine (INO), nitryl iodine (INO2), and iodine nitrate (IONO2) have been produced in situ in the gas phase in a large glass reaction chamber and their infrared absorption spectra were recorded in the range 600-4000 cm-1 at 298 +/- 2 K. This is the first report of the IR gas-phase spectra of these compounds and also the very first report of the IR spectrum of IONO2. IONO2 was observed to decay in the dark with a first-order rate coefficient of approximately 3.2 x 10(-2) s-1 under the experimental conditions of the study. Although it is not clear if the decay is due entirely to thermal decay, it is much higher than the value generally used in model simulations of iodine chemistry in the troposphere; repercussions for the atmospheric iodine cycle are briefly discussed. Nitrogen pentoxide (N2O5) was also a product in the I2-NO2-N2 photolysis system used to produce IONO2. The formation of N2O5 is thought to involve the photolysis of IONO2 to give NO3 radicals, which with NO2 rapidly establish an equilibrium with N2O5: IONO2 + hv --> I + NO3 NO3 + NO2 + M <-> N2O5 + M The possible use of this system as a continuous source of NO3 radicals for laboratory experiments is also considered.