Rate of the OH + C6H6 + He reaction in the fall-off range by discharge flow and OH resonance fluorescence

The rate constant k1 of the reaction[Formula: see text]has been investigated by discharge flow resonance fluorescence of OH in the fall-off pressure range. From systematic measurements at five pressures between 0.5 and 9.5 torr, the Troe parameters k0 and k∞ (with Fc = 0.6) have been derived at two temperatures: room temperature and 353 K. For room temperature, (297 ± 3) K, these parameters are k0 = (1.7 ± 0.5) × 10−29 cm6 molecule−2 s−1, k∞, = (10 ± 2) × 10−13 cm3 molecule−1 s−1. Our experimental results are consistent with addition as the dominant path, in agreement with flash photolysis investigations and with the existence of a fast reaction with NO2 of the (OH—benzene) radical adduct. A numerical simulation shows that this latter reaction should have a rate constant of (4 ± 2) × 10−11 cm3 molecule−1 s−1 at 353 K. Key words: gas phase kinetics, discharge flow, resonance fluorescence, reaction of OH with benzene, tropospheric chemistry.