Spectroscopic and computational analysis of the molecular interactions in the ionic liquid ion pair [BMP]+[TFSI]−

► We investigated interactions between [BMP]+[TFSI]- ion pairs using ab initio method. ► Infrared spectrum of [BMP]+[TFSI]- was assigned using DFT calculations. ► AIM method was employed to analyze the hydrogen bond interactions between [BMP]+[TFSI]- ion pairs. ► NBO analysis was carried out to show the importance of charge transfer interaction between [BMP]+[TFSI]- ion pairs.