Fermi resonances in the vibrational spectrum of perfluoroethane

Abstract In this paper the Raman spectrum of liquid C 2 F 6 in the spectral region 250–1500 cm −1 is presented. Data on six fundamental Raman bands of C 2 F 6 are obtained. Doublets are observed in the spectral regions of the ν 1 ( A 1 g ) (1416.3 cm −1 , 1425.0 cm −1 ) and ν 7 ( E g ) (1221.9 cm −1 , 1239.7 cm −1 ) fundamental bands. The structure of these bands is explained in terms of the Fermi resonances of ν 7  ∼ (2ν 8 ) ∼ (ν 6  + ν 11 ) ( E g ) and ν 1  ∼ (2ν 6 ) ( A 1 g ) states. The values of the cubic potential energy constant K 166  = 7.7 (2) cm −1 and the effective matrix element of a threefold interaction W eff   = 8.5 (5) cm −1 were derived from the simultaneous processing of the doublet parameters in the Raman spectrum of liquid C 2 F 6 and in the IR spectrum of C 2 F 6 in liquid N 2 .