Gas phase electronic absorption spectroscopy of room temperature ionic liquids: N-Ethyl-3-methylpyridinium or 1-butyl-3-methylimidazolium cation with bis(trifluoromethylsulfonyl)amido anion

► Absorption spectra of ionic liquids were measured in gas phase. ► A cavity ring-down technique was applied to gas measurements. ► Vaporization enthalpies were determined from gas absorbance: ► Small spectral shifts in gas are due to large volume of ion pair.