Vibrational Spectra and Dynamics of Anions and Acids in Ionic Liquids

Abstract

Vibrational spectra and energy relaxation lifetimes are reported for the protonated acidic species hydrazoic acid (HN3) and the azide (N3-), thiocyanate (NCS-) and dicyanamide (DCA) anions in imidizolium and phosphonium ionic liquids (ILs). The vibrational spectra and dynamics for the anions in phosphonium tetrafluoroborate and dicyanamide ILs are similar to those previously reported for imidizolium ILs, which resemble the behavior in aprotic molecular solvents such as dimethylsulfoxide. The results are different for hydrazoic acid. In water, methanol and other protic solvents the energy relaxation time is shorter for the azide anion than its protonated and neutral counterpart, hydrazoic acid. In ILs, however, the anion relaxation times are faster than the acid, indicating that the intermolecular interactions are different for acids and anions in ILs compared to conventional molecular solvents.