Absorption cross-section of IO at 427.2 nm and 298 K

The absorption cross-section of the IO radical was determined at a wavelength of 427.2 nm and at a resolution of ≈0.08 nm at room temperature (298 ± 2 K) using the technique of laser photolysis combined with transient absorption spectroscopy. Three previously untested chemical schemes were used to generate calibrated amounts of IO and two of these were used to derive a cross-section of σ 427.2   nm IO = ( 3.55 ± 0.35 ) × 10 − 7   c m 2   molecul e − 1 . The value of σmax, at the peak of the 4,0 band (located at ≈427.08 nm, wavelengths given in air) is ≈8% larger than at 427.2 nm. This result is compared with previous determinations and evaluations. As part of this study the branching ratio (at 298 K) of IO formation from the reactions of O(3P) with CF3I and CH3I were measured as 0.90 ± 0.05 and 0.38 ± 0.05, respectively. Data on the formation and relaxation of vibrationally excited IO in the chemical systems used in this study were also obtained.