Ultra-schnelle Pump-Probe in silico Experimente mit Systemen in kondensierter Phase
Physikalische Chemie von Molekülen, Flüssigkeiten und Grenzflächen, Biophysikalische Chemie
Zusammenfassung der Projektergebnisse
Energy dissipation in water is very fast and more efficient than in many other liquids. This behavior is commonly attributed to the intermolecular interactions associated with hydrogen bonding. Previous condensed phase energy decomposition analysis simulations by us have revealed an asymmetry in the hydrogen-bond network in liquid water, in the sense that a significant population of water molecules are simultaneously donating and accepting one strong hydrogen-bond and another substantially weaker one. Here we investigate this asymmetry, as well as broader structural and energetic features of water’s hydrogen-bond network, following the application of an intense electric field square pulse that invokes the ultrafast reorientation of water molecules. We find that the necessary field-strength required to invoke an ultrafast alignment in a picosecond time window is on the order of 108 Vm^-1. The resulting orientational anisotropy imposes an experimentally measurable signature on the structure and dynamics of the hydrogenbond network, including its asymmetry, which is strongly enhanced. The dependence of the molecular reorientation dynamics on the field-strength can be understood by relating the magnitude of the water dipole–field interaction to the rotational kinetic energy, as well as the hydrogen-bond energy. In addition, we investigate the dynamic energy flow in the hydrogen bond network of liquid water by a pump-probe experiment. We resonantly excite intermolecular degrees of freedom with ultrashort single-cycle terahertz pulses and monitor its Raman response. Therein, background-free bipolar signal whose tail relaxes monoexponentially is obtained. The relaxation is attributed to the molecular translational motions, using complementary experiments, force field, and ab initio molecular dynamics simulations. They reveal an initial coupling of the terahertz electric field to the molecular rotational degrees of freedom whose energy is rapidly transferred, within the excitation pulse duration, to the restricted translational motion of neighboring molecules. This rapid energy transfer may be rationalized by the strong anharmonicity of the intermolecular interactions.
Projektbezogene Publikationen (Auswahl)
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Enhancement of the local asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse. Scientific Reports, 9(1).
Elgabarty, Hossam; Kaliannan, Naveen Kumar & Kühne, Thomas D.
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Energy transfer within the hydrogen bonding network of water following resonant terahertz excitation. Science Advances, 6(17).
Elgabarty, Hossam; Kampfrath, Tobias; Bonthuis, Douwe Jan; Balos, Vasileios; Kaliannan, Naveen Kumar; Loche, Philip; Netz, Roland R.; Wolf, Martin; Kühne, Thomas D. & Sajadi, Mohsen
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Tumbling with a limp: local asymmetry in water's hydrogen bond network and its consequences. Physical Chemistry Chemical Physics, 22(19), 10397-10411.
Elgabarty, Hossam & Kühne, Thomas D.
