Water vapor electron scattering cross-section measurements using a hydrophobic ionic liquid

The interface of ionic liquid (IL) 1-ethyl-3-methylimidazolium-bis-(trifluoromethylsulfonyl)-imide, [EMIM][Tf2N], was examined in the presence of water vapor using lab-based ambient pressure X-ray photoelectron spectroscopy (APXPS) with a monochromatic Al Kα X-ray source. Room temperature water vapor exposures to [EMIM][Tf2N] ranged from 10−6 to 2.0 Torr with no evidence of water uptake at the IL-vapor interface. The hydrophobic nature of [EMIM][Tf2N] allowed for measuring the attenuation of F 1s, O 1s, N 1s, C 1 s and S 2p APXPS peaks as a function of pressure, allowing for the determination of the electron scattering cross-section (σe) of gas phase water. The elemental diversity of [EMIM][Tf2N] allowed for the extraction of σe over a 520 eV kinetic energy range in the absence of a variable energy X-ray source. Herein we show that lab-based APXPS in combination with an elementally diverse, unreactive substrate is an effective tool for the determination of electron scattering cross sections for gas phase species.