Fundamental assignments and molecular properties of CF 2ClBr

Abstract

The fundamental assignments suggested by Plyler and Acquista for difluorochlorobromomethane were re-examined, and new assignments satisfying Rayleigh's rule were recommended. On the basis of the new assignments, the sum of the fundamentals fits in very well with Bernstein's substitution rule, and also the medium intensity band at 977 cm −1 is accounted for very satisfactorily. A normal coordinate calculation was carried out on the basis of the new assignments, which favored our assignment of the 440-cm −1 band to the symmetric ν 4 fundamental rather than to the antisymmetric CF 2 rocking ν 8, as previously suggested by Plyler and Acquista. The calculated values of all the potential constants were compared with those of the corresponding ones in similar substituted halomethanes. They compared very closely, both in magnitude and sign, for all constants but one. This lent further support to the principle of transferability of potential constants. The calculated PED showed considerable coupling among the CCl stretching, the CBr stretching, and the low-lying bending A′ vibrations. The mean square amplitudes of vibration for the bonded and nonbonded atoms, the Coriolis coupling coefficients, and the thermodynamic properties for the ideal gas were calculated on the basis of the new assignments.