Ionic Vapor: What Does It Consist Of?

A comprehensive description of room-temperature ionic liquids (RTILs) requires characterization of their properties around normal boiling and critical. Using a thoroughly parametrized force field, we report atomistic simulations of the vapor phase of N-butylpyridinium tetrafluoroborate and 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulphonyl)amide, existing in equilibrium with the liquid phase. We show that in contrast to traditional gases comprised of one type of molecules, the saturated vapor of RTILs consists of a broad range of structures, involving both neutral and charged species. While typically the ionic pair is the most stable vapor structure, the species distribution depends on RTIL chemical composition and is sensitive to temperature and pressure.