Group Additivity for the Band Strength of the CF‐Chromophore for IR‐Photochemistry

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Abstract
Integrated band strengths for rovibrational absorption in the frequency range of the CF‐chromophore (800 to 1300 cm−1) have been obtained from vapour phase IR‐spectra of twelve fluoroalkanes containing one or more CF groups. It is found that the chromophore band strength is about 1.7 (pm)2 for each CF group with some minor variations due to neighbouring substituents at the CF carbon atom. These variations can be accounted for by a simple, empirical equation. The results are discussed in relation to the chromophore principle in IR‐photochemistry. The frequency distribution of the chromophore absorption for primary, secondary, and tertiary alkyl fluorides is considered. The primary CF‐chromophore (R ‐ CH2 ‐ F) is suggested to be a particularly useful general chromophore for CO2‐laser pumping. The foundations of the group additivity for chromophore band strengths and some further applications are discussed as well.

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