Abstract. The kinetics of the title reactions were investigated using the laser photolysis -resonance fluorescence method, employing the sequential two-photon dissociation of NO 2 in the presence of H 2 as the OH source. The 298 K rate constant for OH + C 3 H 8 was found to be (1.15 ± 0.1) × 10 −12 cm 3 s −1 , in excellent agreement with the literature recommendation, and with a separate determination using HNO 3 photolysis at 248 nm as the OH source. The 298 K rate constants for OH + n−C 3 H 7 I and i−C 3 H 7 I were measured for the first time and found to be (1.47 ± 0.08) and (1.22 ± 0.06) × 10 −12 cm 3 s −1 , respectively. The errors include an assessment of systematic error due to concentration measurement, which, for the propyl-iodides was minimised by on-line UV-absorption spectroscopy. These results show that reaction with OH is an important sink for n−C 3 H 7 I and i−C 3 H 7 I, which has implications for the reactive iodine budget of the marine boundary layer.

Abstract. The kinetics of the title reactions were investigated using the laser photolysis - resonance fluorescence method, employing the sequential two-photon dissociation of NO2 in the presence of H2 as the OH source. The 298 K rate constant for OH + C3H8 was found to be (1.15±0.1) × 10-12 cm3 s-1, in excellent agreement with the literature recommendation, and with a separate determination using HNO3 photolysis at 248 nm as the OH source. The 298 K rate constants for OH + n-C3H7I and i-C3H7I were measured for the first time and found to be (1.47±0.08) and (1.22±0.06) × 10-12 cm3 s-1, respectively. The errors include an assessment of systematic error due to concentration measurement, which, for the propyl-iodides was minimised by on-line UV-absorption spectroscopy. The implications of these results for the reactive iodine budget of the marine boundary layer are discussed.