Abstract-Theoretical Study on Electronic and Vibrational Properties of Hydrogen Bonds in Glycine-Water Clusters

• Yulei Shi^a, 
• Zhiyuan Zhang^b, c, 
• Wanrun Jiang^b, c, 
• Zhigang Wang^b, c, , , 

• ^a Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048, China.
• ^b Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
• ^c Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy (Jilin University), Changchun 130012, China

http://www.sciencedirect.com/science/article/pii/S000926141730578X

The hydrogen bond (H-bond) in organic-water molecules is essential in nature, and it present unique properties distinct from those in pure water or organic clusters. Combining with the charge-transfer and energy decomposition analyses, we investigated the penetrating molecular-orbitals in glycine-water clusters, which give evidences of the covalent-like characteristics of H-bonds in this system. Besides, the infrared spectral features provide a rare opportunity to discover the exceedingly-evident redshifts of symmetric stretching modes (Symst) in water on forming H-bond, in contrast to the slightly-redshifted asymmetric stretching modes (Asyst) in water. To explain these intriguing behaviors, we further analyzed the nuclear vibrating patterns, which clearly reveal that H-bond retains two unexpected effects on nuclear motions in water: i) Intensifying donor Symst, and ii) Inhibiting donor Asyst. Furthermore, we also quantified the impact of anharmonic quantum fluctuations on each hydrogen bond. For the stretching modes involved in H-bonds, red shifts up to more than one hundred wave numbers are observed under anharmonic vibration, explicitly indicating the increased “covalency” of H-bonds. These finds shed light on the essential understanding of H-bonding comprehensively, and should provide incentives for future experimental studies

Abstract-Study of asymmetric U-shaped resonator at terahertz frequencies

• Zhou Yang
• Qingli Zhou
• Wen Long
• Chenyu Li
• Yulei Shi
• Ani Wu
• Jianfeng Liu
• Cunlin Zhang

http://www.sciencedirect.com/science/article/pii/S0030401816300906

We demonstrate the asymmetric U-shaped array exhibits different spectral patterns in response to incident terahertz wave with horizontal and vertical polarizations. In the horizontal incident polarization, where terahertz electric-field E_in is in parallel with the bottom bar of U-shaped structure, the two-absorption-dip transmission spectrum is similar to that of a typical split-ring resonator. When E_in is perpendicular to bottom bar, an interesting phenomenon comes up with three dips. This differs from the split-ring resonator which only has one dip in the transmission spectrum. The bottom-bar length also has significant impacts on frequency-shift and absorptive depth related to this resonant phenomenon.

Abstract-Study of L-shaped resonators at terahertz frequencies

Jianfeng Liu^1,2, Qingli Zhou^1,a), Yulei Shi¹, Xu Zhao¹ and Cunlin Zhang¹

1 Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory for Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048, China
2 Beijing NO. 55 Middle School, Beijing 100027, China
a) Author to whom correspondence should be addressed. Electronic mail: qlzhou@cnu.edu.cn.
Appl. Phys. Lett. 103, 241911 (2013); http://dx.doi.org/10.1063/1.4847295

In experimental and theoretical studies of terahertz subwavelength “L”-shaped structure, we proposed an unusual-mode current resonance responsible for low-frequency characteristic dip in transmission spectra. Comparing spectral properties of our designed simplified structures with that of split-ring resonators, we attribute this unusual mode to the resonance coupling and splitting under the broken symmetry of the structure. Furthermore, it is found that this phenomenon is also related to not only the spacing between horizontal and vertical sides but also their relative position in “L” structure, showing the weakened coupling and spectral splitting with the increased distance and structure symmetry.

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