Water Interfaces, Solvation, and Spectroscopy

Abstract

Liquid water consistently expands our appreciation of the rich statistical mechanics that can emerge from simple molecular constituents. Here I review several interrelated areas of recent work on aqueous systems that aim to explore and explain this richness by revealing molecular arrangements, their thermodynamic origins, and the timescales on which they change. Vibrational spectroscopy of OH stretching features prominently in these discussions, with an emphasis on efforts to establish connections between spectroscopic signals and statistics of intermolecular structure. For bulk solutions, the results of these efforts largely verify and enrich existing physical pictures of hydrogen-bond network connectivity, dynamics, and response. For water at interfaces, such pictures are still emerging. As an important example I discuss the solvation of small ions at the air-water interface, whose surface propensities challenge a basic understanding of how aqueous fluctuations accommodate solutes in heterogeneous environments.

Cryogenic ion trap vibrational spectroscopy of hydrogen-bonded clusters relevant to atmospheric chemistry

“…They 'result from attractive interactions, arising from electrostatic, induced and London dispersion forces, between a hydrogen atom from a molecule or a molecular fragment X-H in which X is more electronegative than H …' [1] and govern the properties of protic solvents, a foremost water, as well as the species that are solvated in them [2]. They 'result from attractive interactions, arising from electrostatic, induced and London dispersion forces, between a hydrogen atom from a molecule or a molecular fragment X-H in which X is more electronegative than H …' [1] and govern the properties of protic solvents, a foremost water, as well as the species that are solvated in them [2].…”

“…[15][16][17][18][19][20][21][22][23][24][25][26][27] and references therein). 2 N. Heine and K.R. Recent improvements in this research field are directly linked to the use of cryogenic, temperature-controllable ion traps, which allow for the preparation of thermalised mass-selected ions with variable internal energy [36][37][38][39][40].…”

Mechanism of ion adsorption to aqueous interfaces: Graphene/water vs. air/water

“…Experiments subsequently verified these predictions (3,4). Surface enhancement of simple ions has since been widely studied [e.g., see the review by Jungwirth and Tobias (5)] and attributed to various properties of the ions including size, polarizability, dispersion forces, hydration free energy (6)(7)(8), and the degree of interfacial roughness (9)(10)(11). Previous temperaturedependent deep UV (DUV) second harmonic generation (SHG) experiments from the Saykally group have determined the enthalpic and entropic contributions to the adsorption of the prototypical pseudohalide, the thiocyanate (SCN − ) ion, showing that a negative enthalpy change drives the ion adsorption, whereas a negative entropy change impedes it (9).…”

Untersuchung der Struktur und Dynamik von Wasser an der Wasser‐Luft‐Grenzfläche mittels oberflächenspezifischer Schwingungsspektroskopie

“…Zum Beispiel hat Volumenwasser eine sehr hohe Wärmekapazität, ein sehr komplexes Phasendiagramm und eine sehr große Dielektrizitätskonstante.D ie physikalischen Eigenschaften von Wasser an Grenzflächen unterscheiden sich signifikant von den Eigenschaften des Wassers im Volumen. [163] So ist beispielsweise die Dielektrizitätskonstante von Grenzflächen-wasser zehnmal niedriger als im Volumen, die Oberflächen-spannung der Wasser-Luft-Grenzfläche ist (im Vergleich zu anderen Flüssigkeiten) extrem hoch und das Phasendiagramm von Wasser an Grenzflächen unterscheidet sich signifikant von dem im Volumen. [4,5] Zusätzlich zum grundlegenden Interesse an den genannten Eigenschaften zeigt sich, dass das Verständnis dieser Merkmale entscheidend ist für wichtige Felder wie beispielsweise Elektrochemie,O berflä-chenchemie atmosphärischer Aerosole,C hemie der Mineralien/Wasser-Grenzfläche,B iophysik von Membranen sowie makroskopische Phänomene wie die Bewegung von Insekten über die Wasseroberfläche (z.…”