Photodecomposition of iodopentanes in air: Product distributions from the self-reactions of n-pentyl peroxyl radicals

Product distributions from the 254-nm photooxidation of the three iodopentane isomers were explored as a technique for studying the self-reactions of individual pentyl peroxyl radicals (in air at ambient temperature and pressure). Pentanols and the associated carbonyl compounds (pentanal or pentanones) were major products as expected. Other major products resulted from the isomerization of pentan-1-oxyl and pentan-2-oxyl radicals, but their nature could not be identified. Minor products were alcohols and carbonyl compounds arising from the decomposition of pentoxyl radicals. Diols and mixed hydroxycarbonyl compounds from cross-combination reactions were essentially absent, in contrast to expectation. The observed product distributions were evaluated to derive branching ratios for the radical-preserving pathways of the self-reactions, 0.42 ± 0.17, 0.46 ± 0.10, 0.39 ± 0.08, for pentan-1-yl peroxyl, pentan-2-yl peroxyl, and pentan-3-yl peroxyl, respectively. Rate coefficients derived for the decomposition of the corresponding pentoxyl radicals, relative to their reaction with oxygen, are (5.1 ± 0.5) × 1018, (1.0 ± 0.2) × 1018, and (3.2 ± 0.3) × 1018 molecule cm-3, respectively. Rate constants for the isomerization of pentan-1-oxyl and pentan-2-oxyl were estimated from the contributions of isomerization products to the total amounts of products as (4.0 ± 1.1) × 105 s-1 and (1.0 ± 2.0) × 105 s-1, respectively.