Laser induced fluorescence of IO radicals and rate constant for the reaction of IO+NO

Abstract

The first observation of laser‐induced fluorescence of the IO free radical in the gas phase is reported. The source of ground‐state IO (X 3Π3/2) radicals was the photolysis of the O3–HI mixture by KrF (248 nm) and N2O–HI mixture by ArF (193 nm) excimer laser radiation. Laser excitation spectra involving the vibrational levels of the A 2Π3/2 state were measured, using excitation wavelengths varying from 440–470 nm from a YAG‐pumped dye laser. The laser excitation spectra of the 2‐0 and 0‐0 band were observed, while the 1‐0 band was not observed due to strong predissociation. The lifetimes of v′=2 and v′=0 levels in the A 2Π3/2 state were shorter than 10 ns. This means that predissociation occurs also in both levels. Each rotational level in the v′=2 and v′=0 levels is affected by predissociation;predissociation occurs more strongly in the higher J levels. The rate constant for the reaction of IO+NO→I+NO2 was measured by the addition of NO to the N2O–HI system. The rate constant obtained is (2.8±0.2)×10−11 cm3 molecule− 1 s−1, 1.6 times faster than the value reported by Ray and Watson.