Photoelectron spectroscopy from a liquid jet of aqueous solution combines a gas phase environment (the Knudsen layer of evaporating/condensing water molecules that surround the jet) with that of a (liquid) surface (Fig. , left hand side). The vacuum the example schematic energy diagra the case where the work function o greater than that of the analyzer [(f wat conditions IE meas water is lower than IE r w adequate reference IEs exist in the l tions this effect would not be immed menter. A quantifiable observable is conditions is also lower than IE real gas (fo is available ), because the gas re electric field that affects all its energy 1s core level equally, see Fig. ). One determine if the work function of an (IE meas gas o IE real gas ) or smaller (IE meas gas analyzer by comparing the IE of gas p in the presence of the aqueous solut levels of the aqueous solution and an traditionally assumed for the interp measurements, then IE meas gas = IE real gas an