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

Ultraviolet absorption spectra of ionic liquids, N-ethyl-3-methylpyridinium bis(trifluoromethylsulfonyl)amido (EmpyTf2N) and 1-butyl-3-methylimidazolium Tf2N (BmimTf2N) were measured in the gas phase by a cavity ring-down and a conventional single-path absorption methods. The vapor pressures at 400–430 K were derived from the measured absorbance, and the vaporization enthalpies were determined as 162 ± 35 and 137 ± 11 kJ mol−1 for EmpyTf2N and BmimTf2N, respectively. There are no remarkable spectral shifts between the absorption spectra in gas phase and neat liquid conditions, which are discussed based on the solvation model of the Onsager reaction field.