Isotopic Fractionation in Photolysis of Ozone in the Hartley and Chappuis Bands

Chao Hui Huang, S. K. Bhattacharya, Zhi Ming Hsieh, Yu Jung Chen, Tai Sone Yih, Mao Chang Liang

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The isotopic enhancement of atmospheric ozone (O3) is mainly determined by two processes of formation and photolytic decomposition. The formation is known to be associated with isotopic fractionation which can be as high as 120‰ relative to the parent oxygen. Photolysis-induced isotopic fractionation in O3, however, is not known accurately. Absorption cross sections of various ozone species have been calculated by Zero Point Energy-based model and quantum mechanical wave packet model. But their predictions pertaining to isotopic fractionations have not been verified experimentally. In the present work, we performed irradiation experiments of O3 at several wavelengths in the Hartley and Chappuis bands and determined the dissociative isotopic fractionation factors by a Rayleigh distillation model. In laboratory conditions, photolysis of ozone produces reactive atomic and/or molecular oxygen which influence the dissociative process through secondary chemistry. The complex interplay of primary photolysis and secondary chemistry was tracked by a kinetic model, and isotopic fractionation factors associated with photolysis alone were derived within a range of uncertainties. The fractionations are found to depend on the photon wavelength and deviate significantly at some wavelengths from the predicted values. For example, at 254 nm the zero point energy-based models predict lower photolysis rate coefficients for the lighter isotopic species; the present data show about 50‰ higher values.

Original languageEnglish
Pages (from-to)752-773
Number of pages22
JournalEarth and Space Science
Volume6
Issue number5
DOIs
StatePublished - May 2019

Keywords

  • isotopic fractionation
  • mass-independent fractionation
  • ozone photolysis

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