Updating the Chemiluminescence Oxygen-Aftereffect Method for Determining the Rate Constant of the Peroxy-Radical Self-Reaction: Oxidation of Cyclohexene.

Updating the facile chemiluminescence oxygen-aftereffect method, most suitable for determining the rate constant (kt ) of the peroxy-radical self-reaction (main chemiluminescence channel), pertained to considering the sensitivity of such a method toward a disturbing influence of the peroxy radicals of the initiator of the chain oxidation process. Such a disturbance may derive from the side chemiluminescent reaction, which involves peroxy radicals of both hydrocarbon and initiator. To examine the applicability and limitations of the chemiluminescence method under present scrutiny, cyclohexene was used as the model oxidizable hydrocarbon substrate. Computer simulations of the reaction and chemiluminescence kinetics have demonstrated the validity of the considered methodology at the value of the rate constant of the propagation of the overall chain process by peroxy radicals of the initiator higher than 1 m-1 s-1 . Despite that the chemiluminescence time profile and the stationary level of the total chemiluminescence intensity depend on the kinetics of the side chemiluminescence channel and on the ratio of the excited-state generation yields in the mentioned reaction channel and in the main chemiluminescence process, the value of kt assessed by the oxygen-aftereffect method has been found independent of variation of these characteristics.

Chemiluminescence of Cigarette Smoke: Salient Features of the Phenomenon.

The study disclosed herein provides for the first time a detailed experimental support for the general mechanism of the cigarette-smoke-derived chemiluminescence, as an example par excellence of the excited-state generation in a chemically complex aerosol medium. The mechanism involves chemiexcitation in a unimolecular transformation of the smoke-borne free radical species. However, the concentration of these radicals, [r∙], obeys a bimolecular (second-order) kinetics and depends on a particulate-phase content (total particulate matter, TPM) of the cigarette smoke. The decrease in [r∙] with increasing the TPM amount manifests radical-scavenging propensity of the smoke particulate phase. Astonishingly, no energy transfer takes place from the primary excited light-emitting species to luminophoric molecules abundant in the smoke. The reported results build up fundamentals of a facile chemiluminescence assay for free radical properties of the smoke. The experimental approaches developed for this study are of general scope and may be used for mechanistic elucidation of the excited-state generation in chemical systems and environments of an arbitrary complexity.