Water/methanol solutions characterized by liquid μ-jet XPS and DFT—The methanol hydration case

Abstract

SynopsisThe electronic structure of water and methanol as vapours, liquids, as well as liquid mixture is determined using synchrotron-based X-ray photoemission spectroscopy on liquid μ-jets.These results together with density functional theory provide, among others, interesting insight into the hydration of these two molecules in the liquid phase mixture.Abstract The advent of liquid μ-jet setups as proposed by Faubel and Winter -in conjunction with X-ray Photoemission Spectroscopy (XPS) -has opened up a large variety of experimental possibilities in the field of atomic and molecular physics. In this study, we present first results from a synchrotron-based XPS core level and valence band electron spectroscopy study on water (10 -4 M aqueous NaCl solution) as well as a water/methanol mixture using the newly commissioned ALBA liquid μ-jet setup. The experimental results are compared with simulations from density functional theory (DFT) regarding the electronic structure of single molecules, pure molecular clusters, and mixed clusters configurations as well as previous experimental studies. We give a detailed interpretation of the core level and valence band spectra for the vapour and liquid phases of both sample systems. The resulting overall picture gives insight into the water/methanol concentrations of the vapour and liquid phases as well as into the local electronic structure of the pertinent molecular clusters under consideration, with a special emphasis on methanol as the simplest amphiphilic molecule capable of creating hydrogen bonds.

A Direct Probe of the Hydrogen Bond Network in Aqueous Glycerol Aerosols

“…Therefore, our two-peak Gaussian analysis for the gas phase and the condensed phase peaks have the contribution from both glycerol and water. Our analysis is in good agreement with literature 39 in the case of BE shifts and peak positions (540 and 538.5 eV) when we compare the gas and condensed phase component as shown for pure water superimposed on the 1 mol% data of the O 1s spectrum. Given our experimental resolution, we focus on the intensity changes as a function of glycerol mol% fraction, rather than BE shifts, to gain insight into the change in the hydrogen bond network.…”

“…Because these experiments were performed with highly volatile alcohols, in contrast to glycerol, the gas phase component was comparatively large and dominated the total spectral distribution. Typically, the BE shift between gas and the condensed phase is around ∼2 eV with the gas phase having a larger binding energy . In Figure A, we fitted the experimental data with two Gaussians to represent the gas (292 eV) and condensed phase (290.5 eV) component, and the sum shows the fit to the experimental data reasonably well, apart from the region between 296 and 294 eV.…”

“…Typically, the BE shift between gas and the condensed phase is around ∼2 eV with the gas phase having a larger binding energy. 39 In Figure 1A, we fitted the experimental data with two Gaussians to represent the gas (292 eV) and condensed phase (290.5 eV) component, and the sum shows the fit to the experimental data reasonably well, apart from the region between 296 and 294 eV. To account for that, we have used a three-peak fit which is shown in the Supporting Information (SI 1).…”

“…A spectrum is superimposed on the 1.0 mol % spectrum showing gas phase (540 eV) and condensed phase (538 eV) peaks of pure water. (From ref ) Solid and dashed lines indicate the condensed phase and gas phase BE positions, respectively.…”

Characterization of Charge States in Conducting Organic Nanoparticles by X-ray Photoemission Spectroscopy

“…XPS has been traditionally limited to the ultrahigh vacuum (UHV) environment (below 10 −9 mbar) in order to strongly reduce surface contamination and to allow the photoelectrons to reach the analyzer within several cm (distance sample-entrance cone of the analyzer). However, the use of XPS has been boosted in the last years thanks to the advent of analyzers that can operate in near-ambient conditions (in the mbar regime), thus allowing the studies of surfaces in more realistic experimental conditions by reducing the so-called pressure gap, the several orders of magnitude difference between UHV and typical industrial conditions [6][7][8]. In this case, the sample-entrance cone must be reduced to 1 mm or less.…”