| Abstrakt: |
Following the discovery of strong oxygen isotope enrichment in stratospheric O3 and in particular the puzzling concomitant large excess enrichment in 17O, more atmospheric gases, importantly CO2 and CO, have been found to suffer from this effect, known as mass independent fractionation. Understanding this new category of isotope effects, which for O3 appears to be a rare, symmetry related kinetic isotope effect, is of fundamental importance. Moreover, the search for the presence of mass independent fractionation effects in atmospheric trace gases and understanding their causes is of interest to atmospheric chemistry. Conventional accurate oxygen isotope ratio analysis is based on mass spectrometry of CO2. However, using CO2 does not allow measurement of the 17O/16O ratio due to isobaric interference from 13C variations. Therefore, conversion to O2 is necessary, for which a fast and safe method has been developed. The essence of the new method is that CO2 is first converted to H2O and CH4 by reacting it with H2. To increase reaction speed and to achieve quantitative conversion, a Ni powder catalyst is used at its Curie point. Subsequently, the formed H2O readily reacts with F2 to form the desired O2 with HF as waste product. A safe reaction is assured by using a mixture of only 5% F2 in He. The validity of the produced isotope ratios is verified independently. © 1998 John Wiley & Sons, Ltd. |
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