INFRARED-SPECTRA AND STRUCTURE OF PERFLUORO-NORMAL-ALKANES ISOLATED IN NORMAL-ALKANE MATRICES PREPARED BY VAPOR-DEPOSITION

Perfluoro-n-alkane chains (n-CnF2n+1, n = 14, 16, 20, and 24) diluted in n-alkane matrices have been prepared in the form of amorphous films by means of low-temperature vapor deposition. Annealing then films leads to conformational ordering of both kinds of chains. Because of reduced intermolecular interaction between the perfluoro-n-alkane chains, narrow infrared bands result. This has allowed the observation of many intense bands in the 1100-1300-cm-1 region that have not previously been resolvable. The intensities and frequencies of C-F stretching bands found in the El zone-center region of the nu-3 band vary with the chain length. These bands have been assigned, and their unusual intensity distribution in the zone-center region has been accounted for on the basis of a simple coupled oscillator model. Our study shows that the isolated perfluoro-n-alkane chains are highly ordered and persist as helices.