@article{Court:2006:10.1016/j.gca.2005.10.017,
author = {Court, RW and Sephton, MA and Parnell, J and Gilmour, I},
doi = {10.1016/j.gca.2005.10.017},
journal = {Geochimica et Cosmochimica Acta},
pages = {1020--1039},
title = {The alteration of organic matter in response to ionising irradiation: Chemical trends and implications for extraterrestrial sample analysis},
url = {http://dx.doi.org/10.1016/j.gca.2005.10.017},
volume = {70},
year = {2006}
}

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TY  - JOUR
AB  - Ionising radiation is an energy source capable of generating and altering complex organic matter. A full understanding of the radiolytic formation and devolution of organic matter is essential to appreciate the budget of organic chemicals that exist in cometary and interstellar ices, carbonaceous meteorites, and to understand the results of analyses of irradiated extraterrestrial organic matter, such as that in cometary nuclei. The effects of ionising radiation on a set of 10 naturally occurring, terrestrial organic assemblages have been revealed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), carbon isotopic analysis, and stepped combustion-isotope ratio mass spectrometry (SC-IRMS). Progressive radiolytic alteration of biogenic complex-hydrocarbon mixtures induces a decrease in the average size and extent of alkylation of polyaromatic hydrocarbons (PAH) and an increase in the abundance of oxygen-containing compounds, as indicated by Py-GC-MS, and an enrichment in C-13. These changes are attributed to reactions with free radicals, produced by ionising radiation. In contrast, the progressive radiolytic alteration of bitumens proposed to have derived from the radiolytic polymerisation of methane into an organic solid produces, upon pyrolysis, PAH of increasing average size and degree of alkylation. This, the opposite of the trend observed in the irradiated complex-hydrocarbons mixtures, cannot be explained in terms of the radiolytic alteration of a pre-existing array of complex organic molecules. Instead, it suggests the gradual construction of PAH from smaller molecules, supporting the hypothesis of a methane origin. Radiolytic alteration is also associated with a previously unrecognised increase in the mean combustion temperature of organic matter. This leads to predictions regarding the combustion characteristics of the irradiated organic matter present on cometary nuclei. A full understanding of the relationship between the combustion characteristics
AU  - Court,RW
AU  - Sephton,MA
AU  - Parnell,J
AU  - Gilmour,I
DO  - 10.1016/j.gca.2005.10.017
EP  - 1039
PY  - 2006///
SP  - 1020
TI  - The alteration of organic matter in response to ionising irradiation: Chemical trends and implications for extraterrestrial sample analysis
T2  - Geochimica et Cosmochimica Acta
UR  - http://dx.doi.org/10.1016/j.gca.2005.10.017
VL  - 70
ER  - 

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