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 ф1R and ф2R 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 ф1R and ф2R 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.