Fourier-transform IR spectroscopic observation of gaseous nitrosyl iodine, nitryl iodine, and iodine nitrate

Using the photolysis of I[sub 2]-NO[sub x]-N[sub 2], mixtures the nitrogen oxyiodines nitrosyl iodine (INO), nitryl iodine (INO[sub 2]), and iodine nitrate (IONO[sub 2]) 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 600-4,000 cm[sup [minus]1] at 298 [plus minus] 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 IONO[sub 2]. IONO[sub 2] was observed to decay in the dark with a first-order rate coefficient of [approximately] 3.2 [times] 10[sup [minus]2] s[sup [minus]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 (N[sub 2]O[sub 5]) was also a product in the I[sub 2]-NO[sub 2]-N[sub 2] photolysis system used to produce IONO[sub 2]. The formation of N[sub 2]O[sub 5] is thought to involve the photolysis of IONO[sub 2] to give NO[sub 3] radicals, which with NO[sub 2]more » rapidly establish an equilibrium with N[sub 2]O[sub 5]. The possible use of this system as a continuous source of NO[sub 3] radicals for laboratory experiments is also considered.« less