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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Nano-solvation in Hydrogen-Bonded Clusters

Awarded: NOK 6.5 mill.

Project Manager:

Project Number:

205512

Application Type:

Project Period:

2011 - 2017

Water in its liquid and solid forms is held together by hydrogen bonds. When a compound is dissolved in water, some of these break up, while some of the liberated water molecules settle around the molecules of the solute (dissolved compound). Within this project we have investigated this solution process. Instead of studying aqueous solutions, we have studied clusters of water molecules. Such clusters (nanodroplets) consist of a small number of water molecules (H2O)n, where the number n lies between 1 and 1000, and clusters are suitable models of aqueous solutions when we also add a molecule of the dissolved substance (M) whereupon the cluster has the chemical formula M(H2O)n. In our endeavours we determine the geometric structure of such clusters by mass spectrometry, photoelectron spectroscopy and quantum chemical calculations. Water clusters are prepared either by dispersion (by spraying an aqueous solution through a thin capillary tube) or by adiabatic expansion of a gas mixture. The experimens are carried out in a vacuum chamber. Alcohols (ROH), like water, form hydrogen bonds, and alcohol clusters, M(ROH)n, correspond to alcoholic solutions at the nano level. By investigating the effect of gradually adding one and one molecule to the solute molecule of the solvent (water or alcohol), we better understand the relationship between the properties of the molecules in vacuum and their properties in solution. In this project we have asked and answered the following questions: What is the preferred geometric structure of a given cluster? Are molecules of the solute contained within the cluster or at the surface? What are the properties that determine how fast protons migrate in water and in water clusters? How does solvation affect chemical reactivity? How do the external conditions (pressure temperature, gas velocity) affect cluster formation? How can we develop new experimental methods for cluster studies? The project has resulted in 16 publications in journals, paid the salaries of one Ph.D. student and one postdoctoral fellow, led to extensive international cooperation, and not the least provided important answers to basic scientific questions relevant to technology, the chemistry of the atmosphere and climate.

Water-based clusters are elusive objects that play important roles in natural processes and particularly in the atmosphere. Moreover, as our understanding of the structure of the most important of all liquids, water, is still in the making, so is even mor e a fundamental understanding of water as a solvent of ions, molecules and protolytes. In this context, clusters may provide useful stepping stones, by allowing for a gradual transition from the molecule to a micrometer-sized drop. Equally convenient; it opens for investigations by gas-phase experimental techniques. This project adopts the very powerful approach of subjecting similar or even the same cluster systems to both local probing, by means of inner-shell electron spectroscopy (XPS), and to size-di fferentiated reactivity probing, by means of mass spectrometry (MS). The final trait of the project is the application of large-scale quantum chemical and dynamical modeling, in order to (i) obtain independent structural information of the present cluster systems, (ii) provide reaction enthalpies for evaporative process, to be compared to results from MS, and , most extensively, (iii) for accurate simulation of core-level spectra, thus significantly enhancing the interpretation of the experimental spectra by obtaining structural and stability information about the clusters to be studied experimentally. The project benefits from expertise in MS- and XPS-probing of molecular clusters that has been built up over the past decade in Oslo and Bergen, in additio n to a large research network. While the present project is planned in terms of instrumentation existing locally in Oslo and at the MAX-II synchrotron laboratory in Lund, we are preparing to build a new instrument with a mass spectrometric front end whi ch will make it possible to store and size-select clusters prior to spectroscopic measurement. If successful, this platform will allow for close scrutiny of critical questions that are bound to accompany the results

Publications from Cristin

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FRINATEK-Fri prosj.st. mat.,naturv.,tek