The gas‐phase decomposition of alkoxy radicals

Abstract

AbstractIt is shown that it is possible to obtain good data for the rate constant for the decomposition of alkoxy radicals [RO] by using nitric oxide as a radical trap. Two experimental systems have been used.The first system involves the use of dialkyl peroxides [(RO)2] as thermal sources of alkoxy radicals. The peroxide concentration was ∼10−4M, nitric oxide ∼2 × 10−4M, and the extent of reaction was ∼10%. The total pressure was altered using carbon tetrafluoride as an inert gas. The mechanism is equation image Hence R2/R3 = k2[NO]/k3. Our previous studies show that k2 lies in the range 1010.3±0.2M−1·sec−1.The second system employs alkyl nitrites [RONO] as a thermal source of alkoxy radicals. The experimental conditions are very similar, except that we chose to use an atmosphere of nitric oxide for initial experiments. If anything nitric oxide appears to be superior to carbon tetrafluoride as an energy transfer agent. The mechanism is equation image Hence R3 = k1'k3[RONO]/(k3 + k2 + k6 [NO]).Results are given for R = t‐Am, s‐Bu, t‐Bu, i‐Pr, Et, and Me. In addition the first unequivocal evidence is given for the pressure dependence of k3 when R = t‐Bu. The implications for atmospheric chemistry and combustion are also discussed.