Absolute rate constants for the reactions of hydroxyl radicals with benzene (1), benzene‐d6 (2), and naphthalene (3) have been obtained using excimer laser photolysis to generate OH and time resolved resonance fluorescence as its monitor. Reaction (1) was studied at total pressures between 1.5 and 112 mbar at 298 K using Ar as a diluent gas. k1 is found to increase with pressure up to –40 mbar, but to be essentially pressure independent at still higher pressures, k 1∞ (298 K) = (7.0 ± 1.5) 1011 cm3/mol · s. The temperature variation of k1 as studied over the range 244 – 24 K. At temperatures below 330 K normal Arrhenius behaviour with k1 (T) = (3.8 ± 1.0) 1012 exp[‐(500 ± 50) K/T] cm3/mol · s is observed, corresponding to the addition reaction (1) OH + C6H6 → C6H6OH. Between 330 and 420 K a sharp decrease of k1 with increasing temperature is noted, which we attribute to reaction (1) becoming reversible. For the stabilization energy of C6H6OH we derive (79 ± 6) kJ/mol. Above 420 K a transition of k1 to a positive temperature dependence, corresponding to the abstraction reaction (1') OH + C6H6 → H2O + C6H5 is noted. Rate constants for the reaction of OH with benzene‐d6 (2) are essentially identical to those of reaction (1) except for temperatures above 420 K, where k2 falls considerably below k1. This isotope effect is a confirmation of the (1') abstraction route. Reaction (3) was studied at total pressures between 6 and 128 mbar (He) where it is found to be essentially pressure independent. Its temperature variation was studied between 337 and 525 K. Over this region the rate coefficient decreases from (8.8 ± 3.5) 1012 cm3/mol · s to (6.6 ± 2.6) 1011 cm3/mol · s, with the decrease with temperature being relatively weak up to 410 K, k1(T ≤ 410 K) = (2.2 ± 1.0) 1012 exp[(440 ± 50) K/T] cm3/mol · s, and stronger at still higher temperatures. This behaviour is interpreted as to correspond to the addition reaction (3) OH + C10H8 → C10H8OH and its equilibration. The stabilization energy of the OH‐naphthalene adduct is estimated to be (95 ± 6) kJ/mol.

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Rate constants for the reactions (1) CH3O (methoxy) + O2 and (2) CH2CHO (vinoxy) + O2 have been determined between 300 and 500 K using a combined laser photolysis/laser induced fluorescence technique. Whereas reaction (1) is purely bimolecular with k1 = (5.5 ± 2.0) 10−14 exp(−1000 K/T) cm3s, reaction (2) appears to be a recombination process. For p = 130 mbar (M = He) we find k2 = (2.7 ± 1.5) 10−14 exp(668 K/T) cm3s, corresponding to a T−1.8 negative temperature dependence.

Absolute rate constants and CH,O product yield for the reaction of OH radicals with methanol have been determined using a combined laser photolysis/resonance fluorescence (laser induced fluorescence) technique. The rate coefficient for total OH (k, = k, + k2) is found to be k, = (1.2 i 0.3). lo-" exp[-(810 * 50) K/T] cm3/molecule. s over the temperature range 295-420 K. -The branching ratio of CH,O formation, 9 = k, /k, + k,, where (1) OH + CH,OH -+ CH,O + H,O and (2) OH + CH,OH -+ CH20H + H,O, is found to be 0. 1 1 f 0.03 and 0.22 f 0.07 at 298 and 393 K, respectively. From the temperature dependence of 9 it is predicted that channel (1) is dominant in the combustion temperature region.

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