Infra-red and Raman band shapes and dynamics of molecular motions for N₂O in solution: ν₃ band in CCl₄ and liqud SF₆

Abstract

The vibrational and rotational correlation functions are obtained by Fourier inversion of the infra-red and Raman ν₃ band spectra of N₂O, in very dilute CCl₄ and liquid SF₆ solutions, care being taken to eliminate the hot bands and the spectral slit effect. The vibrational correlation function becomes exponential from 1 to 2 ps on; it is separated from the total correlation functions to obtain the rotational correlation functions ф₁R and ф₂R; its influence is not negligible in the case of the CCl₄ solution, especially for the infra-red. The functions ф_1R and ф_2R have the characteristic shape of an inertial motion at short times and show an exponential decay at long times, even for the SF₆ solution where rotation proves easier than in CCl₄. The relationship between ф_1R and ф_2R proposed by Berne and Harp checks well in CCl₄, less well at long times in SF₆. The easy rotation of the N₂O molecule in SF₆ cannot be interpreted from Gordon's m and j models, nor does a friction model accounting for the inertial effect explain the results for both solutions. However a model which, in the context of the j model, assumes an anisotropic reorientation of the angular momentum at the time of a collision, provides a very good fit with our results for the CCl₄ solution.