Carbon absorption surface species effect

One of the main effects of ion irradiation of frozen gases is the formation of molecular species not present in the original sample as indicated by the appearance of new absorption features in the IR spectra. As stated above, after irradiation of carbon bearing refractory species, complex residues are formed (IPHAC). These have been suggested to be analog materials to that of some planetary surfaces [22]. 

The heat-treated materials are very reactive and are readily reoxidized in the presence of air. For example, the carboxylic acid band at 1725 cm 1 reappears when the sample heated to 600°C is milled in air instead of nitrogen (Figure 9). As expected from the above discusssions, the presence of these new surface species also enhances the absorptions at 1595 and 1245 cm 1. Interestingly, the air and nitrogen milling conditions have different effects on the magnitudes of the 1135 an 1340 cm 1 impurity bands of this carbon black. 

For continuous solids with a shiny surface a specular reflection spectrum is obtained. In principle, the absorption spectrum can be derived from this by the Kramers-Kronig transformation. Examples of this are shown for both PP (Figure 4.4(a)) and polyester (Figure 4.4(b)) samples. Equally good results are obtained from both unfilled and carbon-filled samples. The presence of inorganic fillers does not alter the nature of the spectra and any contribution from the filler appears specular. The presence of glass as a filler has little effect on the spectra. The spectra obtained are adequate for qualitative identification, but there are limitations. Band shapes often appear nnsymmetrical and baselines are uneven. When the surface is not shiny the spectra are weaker and may contain a diffuse component. When there are surface species the reflection spectrum may be unrepresentative of the bulk material. No spectra were obtainable from those carbon-filled samples that did not have shiny surfaces. 

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