The femtosecond optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES) time profiles of [Bmim][PF6], [Bmim][BF4], and [Bmim]I present similar damping oscillations, indicating that their femtosecond OHD-RIKES signals mainly arise from [Bmim](+) cations. Both the femtosecond OHD-RIKES fast Fourier-transform spectra and the Raman spectra of [Bmim][PF6], [Bmim][BF4], and [Bmim]I reveal that the interactions between two [Bmim](+) cations in [Bmim]I are stronger than those in [Bmim][PF6] and [Bmim][BF4].