The non-coincidence effect in highly diluted acetone-CCl I. Experimental results and theoretical predictions 4 binary mixtures

The concentration dependence of the first moments and peak frequencies of isotropic and anisotropic profiles of the υ C=O mode in acetone-CCl 4 binary mixtures is investigated. The emphasis is directed mainly towards the non-coincidence effect in the high dilution range, not accessed in previous experiments. Our results for the relative non-coincidence effect in non-isotopic binary mixtures appear largely consistent with the Logan theory. Moreover, the observation of the υ C=O mode of the naturally present acetone- 13 C=O has been exploited to check the validity of the Logan theory for isotopic mixtures. It is verified that the observation of negative values for the non-coincidence effect, which is strictly related to that of a threshold concentration for the onset of this phenomenon, are artefacts due to the presence of spectral asymmetries in the υ C=O mode.