Anomalous oxygen isotope enrichment in CO2 produced from O+CO: estimates based on experimental results and model predictions

Pandey, Antra ; Bhattacharya, S. K. (2006) Anomalous oxygen isotope enrichment in CO2 produced from O+CO: estimates based on experimental results and model predictions The Journal of Chemical Physics, 124 (23). pp. 234301-234313. ISSN 0021-9606

[img]
Preview
PDF - Publisher Version
190kB

Official URL: http://jcp.aip.org/resource/1/jcpsa6/v124/i23/p234...

Related URL: http://dx.doi.org/10.1063/1.2206584

Abstract

The oxygen isotope fractionation associated with O+CO→CO2 reaction was investigated experimentally where the oxygen atom was derived from ozone or oxygen photolysis. The isotopic composition of the product CO2 was analyzed by mass spectrometry. A kinetic model was used to calculate the expected CO2 composition based on available reaction rates and their modifications for isotopic variants of the participating molecules. A comparison of the two (experimental data and model predictions) shows that the product CO2 is endowed with an anomalous enrichment of heavy oxygen isotopes. The enrichment is similar to that observed earlier in case of O3 produced by O+O2 reaction and varies from 70‰ to 136‰ for and 41‰ to 83‰ for 17O . Cross plot of δ17O and δ18O of CO2 shows a linear relation with slope of ~ 0.90 for different experimental configurations. The enrichment observed in CO2 does not depend on the isotopic composition of the O atom or the sources from which it is produced. A plot of Δ(δ17O) versus Δ(δ18O) (two enrichments) shows linear correlation with the best fit line having a slope of ~ 0.8. As in case of ozone, this anomalous enrichment can be explained by invoking the concept of differential randomization/stabilization time scale for two types of intermediate transition complex which forms symmetric (16O12C16O) molecule in one case and asymmetric (16O12C 18O and 16O 12C17O) molecules in the other. The δ13C value of CO2 is also found to be different from that of the initial CO due to the mass dependent fractionation processes that occur in the O+CO→CO2 reaction. Negative values of Δ(δ13C) (~12.1‰) occur due to the preference of in CO2∗ formation and stabilization. By contrast, at lower pressures ( ~100 torr) surface induced deactivation makes Δ(δ13C) zero or slightly positive.

Item Type:Article
Source:Copyright of this article belongs to American Institute of Physics.
ID Code:67074
Deposited On:28 Oct 2011 11:00
Last Modified:18 May 2016 14:20

Repository Staff Only: item control page