Abstract-Rotational coherence of encapsulated ortho and para water in fullerene-C60 revealed by time-domain terahertz spectroscopy

 

Sergey S. Zhukov, Vasileios Balos, Gabriela Hoffman, Shamim Alom, Mikhail Belyanchikov, Mehmet Nebioglu, Seulki Roh, Artem Pronin, George R. Bacanu, Pavel Abramov, Martin Wolf, Martin Dressel, Malcolm H. Levitt, Richard J. Whitby, Boris Gorshunov,  Mohsen Sajadi 

https://www.nature.com/articles/s41598-020-74972-3

We resolve the real-time coherent rotational motion of isolated water molecules encapsulated in fullerene-C60 cages by time-domain terahertz (THz) spectroscopy. We employ single-cycle THz pulses to excite the low-frequency rotational motion of water and measure the subsequent coherent emission of electromagnetic waves by water molecules. At temperatures below ~ 100 K, C60 lattice vibrational damping is mitigated and the quantum dynamics of confined water are resolved with a markedly long rotational coherence, extended beyond 10 ps. The observed rotational transitions agree well with low-frequency rotational dynamics of single water molecules in the gas phase. However, some additional spectral features with their major contribution at ~2.26 THz are also observed which may indicate interaction between water rotation and the C60 lattice phonons. We also resolve the real-time change of the emission pattern of water after a sudden cooling to 4 K, signifying the conversion of ortho-water to para-water over the course of 10s hours. The observed long coherent rotational dynamics of isolated water molecules confined in C60 makes this system an attractive candidate for future quantum technology.

Abstract-Energy transfer within the hydrogen bonding network of water following resonant terahertz excitation

1. Hossam Elgabarty, 
2. Tobias Kampfrath, 
3. Douwe Jan Bonthuis, 
4. Vasileios Balos, 
5. Naveen Kumar Kaliannan, 
6. Philip Loche, 
7. Roland R. Netz, 
8. Martin Wolf, 
9. Thomas D. Kühne,  
10. Mohsen Sajad

https://advances.sciencemag.org/content/6/17/eaay7074.full

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. Here, 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. By using ultrathin sample cell windows, a 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.

Abstract-Terahertz-magnetic-field induced ultrafast Faraday rotation of molecular liquids

Vasileios Balos, Genaro Bierhance, Martin Wolf, and Mohsen Sajadi

https://journals.aps.org/prl/accepted/fa073Y60Xd41a265164477f66ca727873f379d22d

Rotation of the plane of the polarization of light in the presence of a magnetic field, known as the Faraday rotation, is a consequence of the electromagnetic nature of light and has been utilized in many optical devices. Current efforts aim to realize the ultrafast Faraday rotation on a sub-picosecond time scale. To this end, the Faraday medium should allow an ultrafast process by which in the presence of an ultrashort intense magnetic field, the light polarization rotates. We meet the criteria by applying an intense single cycle THz magnetic-field to simple molecular liquids and demonstrate the rotation of the plane of polarization of an optical pulse traversing the liquids on a sub-picosecond time scale. The effect is attributed to the deflection of an optically induced instantaneous electric polarization under the influence the THz magnetic field. The resolved Faraday rotation scales linearly with the THz magnetic field and quadratically with the molecular polarizability.