Far infra-red absorption of disubstituted propanes in rotator, solid and liquid phases

Abstract

Experimental observations of the far infra-red (f.i.-r.) absorption spectra of three polar di-substituted propanes (2,2-dichloro-, 2-chloro-2-nitro-, 2-methyl-2-nitro-propane) over the temperature range 133–303 K in the liquid, rotator and non-rotator solid phases are reported. The spectra in both the liquid and rotator phases are discussed in terms of two simple theoretical models of librational and relaxational motions: an acceptable fit to the experimental spectra is obtained on the basis of reasonable barriers and other parameters of the molecular motion. One of the models indicates that the molecular librational potential wells may become narrower with decreasing temperature and that there may be a distribution of potential well depths or shapes. The variation of potential barrier height with group substitution is also discussed.