Reaction of atomic oxygen with cyclopentadiene

The reaction of 1,3‐cyclopentadiene (CPD) with ground‐state atomic oxygen O( 3 P ), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C 4 H 6 isomers: 3‐methylcyclopropene, 1,3‐butadiene, 1,2‐butadiene, and 1‐butyne. The yield of carbon monoxide over oxygen atoms produced (ϕ CO ) was equal to the sum of the yields of C 4 H 6 isomers in any experiment. ϕ CO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C 5 H 6 O isomers. It was found that 3‐methylcyclopropene was produced with excess energy and was partly isomerized to other C 4 H 6 isomers, especially to 1‐butyne. The excess energy was estimated to be about 50 kcal/mol. The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans ‐2‐butene and 1‐butene. The ratios k CPD+O / k trans‐2‐butene+O = 2.34 and k CPD+O / k 1‐butene+O = 11.3 were obtained. Probable reaction mechanisms and intermediates are suggested.