IR-anregungsmodulierte Photoionisationsspektroskopie an natriumdotierten Wasserclustern

IR Excitation-modulated Photoionization Spectroscopy on Sodium-doped Water Clusters

by Florian Zurheide
Doctoral thesis
Date of Examination:2021-03-25
Date of issue:2021-10-19
Advisor:Prof. Dr. Thomas Zeuch
Referee:Prof. Dr. Thomas Zeuch
Referee:Prof. Dr. Dietmar Stalke
Persistent Address: http://dx.doi.org/10.53846/goediss-8890

 

 

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Abstract

English

The compound water exhibits a variety of unique properties which are indispensable for many processes in animate and inanimate nature. These properties do not arise from a single water molecules but from the strong anisotropic interactions present between numerous water molecules, namely hydrogen bonds. In this work, infrared spectra of water clusters generated in adiabatic supersonic expansions are obtained in a precisely size selective manner to provide an experimental access to these intermolecular interactions and to serve as a bench mark for computational studies that are aimed to model water properties and microphysical processes occurring e.g. in the course of phase transitions and more specifically condensation processes. In collaboration with theoretical research groups the number of water molecules necessary for a structural change from amorphous to crystal-like cluster structures could be assigned to approximately 90 molecules. At the same time a subtle micro effect arising from the energetic balance between molecules located on the cluster surface and those constituting the core could be observed. Structural optimization of the cluster core to form a thermodynamically stable crystal lattice forces surface-near hydrogen bonds to break leading to an enhanced number of free OH oscillators on the surface of crystal-like particles. Moreover, strong evidence was found for the phase transition between liquid water and ice I in small systems to lose its first-order character and to occur through heterophasic oscillations over time within a certain temperature range.
Keywords: water; clusters; ice; ice crystals; phase transitions; mass spectrometry; infrared spectroscopy; supersonic expansions
 
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