The ab initio and semi-empirical gas phase molecular structures of ionic liquids containing PF₆^- are reviewed and correlated with the results of Raman and infrared experiments. The ab initio results include both Density Function Theory (DFT) and Hartree-Fock (HF) methods using various basis sets. The existence of non-bonded interactions (hydrogen bonds) between PF₆^-  and various imidazolium cations in the gas phase structures correlates with NMR relaxation studies of these and similar ionic liquids. The calculated and experimental vibrational spectra are in excellent agreement and also support the results of other recent physical investigations of ionic liquids. The effects of water on the vibrational spectra of selected ionic liquid systems are also reported. The systematic effects of water addition may prove useful in the future qualitative assessment of ionic liquids.