| AVS 66th International Symposium & Exhibition | |
| Chemical Analysis and Imaging Interfaces Focus Topic | Wednesday Sessions |
| Session CA+NS+SS+VT-WeA |
| Session: | Chemical Analysis and Imaging of Liquid/Vapor/Solid Interfaces I |
| Presenter: | Jordi Fraxedas, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain |
| Authors: | J. Fraxedas, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Spain E. Pellegrin, CELLS-ALBA, Spain V. Perez-Dieste, CELLS-ALBA, Spain C. Escudero, CELLS-ALBA, Spain P. Rejmak, Institute of Physics PAS, Poland N. Gonzalez, CELLS-ALBA, Spain A. Fontsere, CELLS-ALBA, Spain J. Prat, CELLS-ALBA, Spain S. Ferrer, CELLS-ALBA, Spain |
| Correspondent: | Click to Email |
The advent of liquid μ-jet setups, in conjunction with X-ray Photoemission Spectroscopy (XPS), has opened up a plethora of experimental possibilities in the field of atomic and molecular physics [1]. Here, we present a combined experimental and theoretical study of the hydration of methanol at the aqueous solution/vapor interface. These are first experimental results obtained from the new liquid μ-jet setup at the Near Ambient Pressure Photoemission (NAPP) endstation of the CIRCE helical undulator beamline (100–2000 eV photon energy range) at the CELLS-ALBA synchrotron light source, using a differentially pumped SPECS PHOIBOS 150 hemispherical electron energy analyzer [2].The experimental results are compared with simulations from density functional theory (DFT) regarding the electronic structure of single molecules and cluster configurations as well as with previous experimental studies.
Methanol is the simplest amphiphilic molecule capable of hydrogen bonding due to its apolar methyl and polar hydroxyl groups. The results obtained from pure water at 600 eV photon energy emphasize the short range tetrahedral distribution as previously observed for crystalline and amorphous ice. We also find indications for ordering phenomena in water/methanol mixtures by the reduced O1s XPS liquid line width (as compared to pure water), which could be ascribed to the amphiphilic character of the methanol molecule. Regarding the C1s XPS lines, the vapor/liquid peak ratios allow for a quantitative determination of the methanol volume concentrations in both the vapor as well as in the liquid phase, that are corroborated by an analogue analysis of the valence band (VB) spectra. A detailed quantitative analysis of the water/methanol liquid VB XPS spectrum accounting for the photon energy dependence of photoemission cross sections confirms the atomic/orbital characteristics of the methanol molecular orbitals involved in the transitions and their pertinent intensities. From the decomposition of the liquid VB spectrum of the water/methanol mixture together with finite XPS probing depth we derive a methanol volume fraction of 43% for the outer liquid layers as compared to the nominal bulk liquid value of 37.5%. Finally, from the different binding energy (BE) shifts of the water/methanol liquid VB spectrum with respect to that of pure methanol, we develop a CH3OH-(H2O)3 cluster-based model that relates these different BE shifts to the different MO hybridizations within that cluster.
[1] B. Winter, M. Faubel, Chem. Rev. 106 (2006) 1176.
[2] V. Pérez-Dieste, L. Aballe, S. Ferrer, J. Nicolàs, C. Escudero, A. Milán, E. Pellegrin, J. Phys. Conf. Ser. 425 (2013) 072023.