In this study, four 1-butyl-2,3-dimethylimidazolium ionic liquids are analysed by X-ray photoelectron spectroscopy, together with three 1-butyl-3-methylimidazolium ionic liquids. A reliable fitting model for the carbon is region of 1-butyl-2,3-dimethylimidazolium ionic liquids is modified according to established models. The effect of the anion on the electronic environment of the cation is explored based upon the comparison between measured binding energies of nitrogen is and the hydrogen bond acceptor ability. The effect of the cation on the cation-anion interaction is also demonstrated by carefully comparing the hydrogen bond donating ability of different cations, with a definite anion. (C) 2017 Elsevier B.V. All rights reserved.