This contribution due to the workfunction differences, which gives rise to the vacuum levels mismatch between the jet and the analyzer and which was neglected in early experiments, is responsible for noticeable discrepancies in the reported IEs (as illustrated by the water core-level IEs below). Olivieri et al. 12 introduced a procedure designed to extract the true IE wat from the microjet experiments by applying a variable bias to the microjet. The bias shifts the energy levels of the liquid and by measuring the dependence of the measured IEs on the applied bias the true IEs can be extracted. By applying this technique to core ionization of water (specifically, 0.05 M solution of NaCl), the authors 12 determined that in their experiment (ϕ wat -ϕ ana ) equals +0.57 (±0.07) eV and the geometric factor is c = 0.70 (±0.05) eV•V -1 . This means that the bulk and gas-phase peak positions from the zero-bias measurement need to be shifted by 0.57 eV and by 0.40 eV, respectively. The value of 0.57 eV is consistent with the optimal bias of +0. Thus, the interface potential affects not only the absolute value of the bulk IE, but also the shift of the bulk IE relative to the gas-phase IE (∆IE). Therefore, the true, intrinsic ∆IE cannot be taken as a difference between the gas-phase and liquid peaks' maxima from an unbiased microjet spectrum. The effect of the interfacial field on the gas-phase molecules around it is clearly seen from the shift of the gas-phase peak relative to the true gas-phase IE-in Ref. 12 this shift equals 0.41 eV; the microjet value is red-shifted, as expected from Fig. and from the theoretical value of the interface potential 20 (illustrated in Fig. ).