The interactions of a mixture composed by 1-ethyl-3-methylimidazolium ethylsulphate [EMIM][EtSO4] and acetone are investigated. In order to carry out such a study, it is necessary to use the IR and the physico-chemical data recorded of the mixture. Subsequently, by applying the idea of excess thermodynamic functions to spectroscopy, it can be used the concept of excess infrared absorption. This concept is used to study the non-ideality of the mixture and the interactions at microscopic level. First, it is possible to work on the non-ideality plotting the excess infrared absorption ɛE against the wavenumber ʋ (cm-1). Then, the interactions are studied choosing characteristic bands from both substances and analysing how their peaks change depending on the molar fraction of each component. For the [EMIM][EtSO4] are mainly studied the stretching bands at 1014.42, 2979.63 and 3103.06cm-1 corresponding to C5-N1-C2, the CH aliphatic and the CH in the ring respectively among other modes. For the acetone, the peak at 1710.64cm-1 from the carbonyl group is chosen. After the analysis of the deviations of each peak and their behaviour the possible formation of hydrogen bonds among the two molecules is discarded and a relative position of the acetone on top of the ionic liquid molecule is considered. Further, the excess volume is calculated and correlated with the excess infrared absorption so that the macroscopic and the microscopic properties of the mixture can be compared. The different effects that the interactions and the geometrics of the sample have in each level of study, microscopic and macroscopic, are demonstrated.

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