Study on non-dissociative bimolecular reactions characteristic of contact molecular pairs

点击翻译按钮获取中文摘要

Ozone-water complex has been suggested as one of the hydroxyl radical sources in the Earth's troposphere. Complexation with water vapor might change the O_3 photochemistry, which might play a crucial role in the production of hydroxyl radical. We have characterized the spectroscopy of O_3-H_2O complex. In this research, the photochemistry of ozone-water complex isolated in cryogenic matrices was studied. Neon, argon, and krypton were employed as matrix media to study the so-called matrix cage effect and to develop the solid state chemistry to the gas phase reaction. Wavelength dependence of photochemistry was studied by using UV and visible light.Ozone ν_3 fundamental region was chosen to monitor the occurrence of ozone photo-dissociation within the monomer and ozone-water complex, because the ν_3 fundamental of the ozone-water complex was fully separated from the monomer ν_3 band. In a neon matrix, the irradiation by 355 nm led to the decreases of ozone monomer and ozone water complex and to the formation of hydrogen peroxide. Apparently the photo-dissociation of ozone was found to take place even at 355 nm. In argon and krypton matrices, the formation of hydrogen peroxide-water complex was also observed, which is thought to be formed from an inter-cage reaction of cage-exited O(^1D) atom with water dimer in a different cage. A hydrogen peroxide formation yield in a neon matrix is estimated to be almost unity, whereas those in argon and krypton exceed unity because of the inter-cage reaction. We concluded that neon is most appropriate media for studying the photochemistry of ozone-water complex. Wavelength dependence was studied in the solid neon. The 254- and 313-nm irradiations gave the similar results at the 355 nm irradiation, but the 365- and 633-nm irradiation did not induce any photochemical reaction. We will discuss the photochemical mechanism (dependence of wavelength and matrix cage) and the implication of the atmospheric ozone chemistry.