Increased Propensity of I_aq⁻ for the Water Surface in Non-neutral Solutions: Implications for the Interfacial Behavior of H₃O_aq⁺ and OH_aq⁻

By a combination of surface-sensitive photoelectron spectroscopy and molecular dynamics simulations, we characterize the surface propensity of the iodide anion in aqueous solutions at acidic, neutral, and basic conditions (pH = 1, 6.8 and 13). In both experiments and simulations, an increased surface concentration of I⁻ is found in non-neutral solutions. We interpret these findings in terms of I⁻ surface coadsorption with hydronium at low pH and “salting out” of iodide by hydroxide from the bulk solution to the surface at high pH. The present study is thus in accord with the picture of a weak surface adsorption of hydronium and surface depletion of hydroxide, being in sharp contradiction with the interpretation of electrophoretic and titration measurements in terms of strong surface enrichment of OH⁻

Near-Edge X‑ray Absorption Fine Structure Investigation of the Quasi-One-Dimensional Organic Conductor (TMTSF)2PF6

We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3-edges, F K-edge, C K-edge and Se M2/3-edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3-edges of (TMTSF)2PF6 do not exhibit a well resolved spectrum. Surprisingly, the C K-edge spectra contain three well defined peaks exhibiting strong and non-trivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor-anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.Work in Spain was supported by MINECO (Spain) through Grants FIS2012-37549-C05-05, FIS2015-64886-C5-4-P and CTQ2015-64579-C3-3-P, and Generalitat de Catalunya (2014SGR301 and XRQTC). E.C. acknowledges support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496. Special thanks are due to Graduate School of Excellence MAINZ and to Transregio SFB TR49. The crystals were synthesized by the late A. Moradpour. We would like to thank to MAX IV laboratory for providing beam time at I1011 beam line.Peer reviewe

Near-Edge X‑ray Absorption Fine Structure Investigation of the Quasi-One-Dimensional Organic Conductor (TMTSF)₂PF₆

We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L_2/3 edges, F K edge, C K edge, and Se M_2/3 edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)₂PF₆. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L_2/3-edges spectra in (TMTTF)₂AsF₆, the Se M_2/3 edges of (TMTSF)₂PF₆ do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)₂PF₆ and (TMTTF)₂AsF₆ exhibit important differences. In contrast with the case of (TMTTF)₂AsF₆, the F K-edge spectra of (TMTSF)₂PF₆ do not change with temperature despite stronger donor–anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts