Crossover from hydrogen to chemical bonding

Science ◽  
2021 ◽  
Vol 371 (6525) ◽  
pp. 160-164 ◽  
Author(s):  
Bogdan Dereka ◽  
Qi Yu ◽  
Nicholas H. C. Lewis ◽  
William B. Carpenter ◽  
Joel M. Bowman ◽  
...  
Keyword(s):  
Chemical Bonding ◽  
Quantum Chemical ◽  
Spectroscopic Properties ◽  
Experimental Methods ◽  
Strongly Coupled ◽  
Donor Acceptor ◽  
Bond Bending ◽  
High Level ◽  
Two Dimensional Infrared Spectroscopy ◽  
Covalent Chemical Bond

Hydrogen bonds (H-bonds) can be interpreted as a classical electrostatic interaction or as a covalent chemical bond if the interaction is strong enough. As a result, short strong H-bonds exist at an intersection between qualitatively different bonding descriptions, with few experimental methods to understand this dichotomy. The [F-H-F]− ion represents a bare short H-bond, whose distinctive vibrational potential in water is revealed with femtosecond two-dimensional infrared spectroscopy. It shows the superharmonic behavior of the proton motion, which is strongly coupled to the donor-acceptor stretching and disappears on H-bond bending. In combination with high-level quantum-chemical calculations, we demonstrate a distinct crossover in spectroscopic properties from conventional to short strong H-bonds, which identify where hydrogen bonding ends and chemical bonding begins.

scholarly journals Electronic excitations in molecular solids: bridging theory and experiment

2015 ◽  
Vol 177 ◽  
pp. 181-202 ◽  
Author(s):  
Jonathan M. Skelton ◽  
E. Lora da Silva ◽  
Rachel Crespo-Otero ◽  
Lauren E. Hatcher ◽  
Paul R. Raithby ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Molecular Crystals ◽  
Spectroscopic Properties ◽  
Implicit Solvent ◽  
Test Case ◽  
Electronic Excitations ◽  
Solvent Models ◽  
Chemical Techniques ◽  
High Level ◽  
Molecular Calculations

As the spatial and temporal resolution accessible to experiment and theory converge, computational chemistry is an increasingly powerful tool for modelling and interpreting spectroscopic data. However, the study of molecular processes, in particular those related to electronic excitations (e.g. photochemistry), frequently pushes quantum-chemical techniques to their limit. The disparity in the level of theory accessible to periodic and molecular calculations presents a significant challenge when modelling molecular crystals, since accurate calculations require a high level of theory to describe the molecular species, but must also take into account the influence of the crystalline environment on their properties. In this article, we briefly review the different classes of quantum-chemical techniques, and present an overview of methods that account for environmental influences with varying levels of approximation. Using a combination of solid-state and molecular calculations, we quantitatively evaluate the performance of implicit-solvent models for the [Ni(Et4dien)(η2-O,ON)(η1-NO2)] linkage-isomer system as a test case. We focus particularly on the accurate reproduction of the energetics of the isomerisation, and on predicting spectroscopic properties to compare with experimental results. This work illustrates how the synergy between periodic and molecular calculations can be exploited for the study of molecular crystals, and forms a basis for the investigation of more challenging phenomena, such as excited-state dynamics, and for further methodological developments.

scholarly journals Optical Activation Behavior of Ion Implanted Acceptor Species in GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 507-513 ◽  
Author(s):  
B.J. Skromme ◽  
G.L. Martinez
Keyword(s):  
Variable Temperature ◽  
Spectroscopic Properties ◽  
Acceptor Pair ◽  
High Quality ◽  
Shallow Acceptor ◽  
Implantation Damage ◽  
Donor Acceptor ◽  
Optical Activation ◽  
Optical Binding ◽  
Dose Dependent

Ion implantation is used to investigate the spectroscopic properties of Mg, Be, and C acceptors in GaN. Activation of these species is studied using low temperature photoluminescence (PL). Low dose implants into high quality undoped hydride vapor phase epitaxial (HVPE) material are used in conjunction with high temperature (1300 °C) rapid thermal anneals to obtain high quality spectra. Dramatic, dose-dependent evidence of Mg acceptor activation is observed without any co-implants, including a strong, sharp neutral Mg acceptor-bound exciton and strong donor-acceptor pair peaks. Variable temperature measurements reveal a band-to-acceptor transition, whose energy yields an optical binding energy of 224 meV. Be and C implants yield only slight evidence of shallow acceptor-related features and produce dose-correlated 2.2 eV PL, attributed to residual implantation damage. Their poor optical activation is tentatively attributed to insufficient vacancy production by these lighter ions. Clear evidence is obtained for donor-Zn acceptor pair and acceptor-bound exciton peaks in Zn-doped HVPE material.

scholarly journals Polarised Covalent Thorium(IV)- and Uranium(IV)-Silicon Bonds

2020 ◽  
Author(s):  
Benjamin Reant ◽  
Victoria E. J. Berryman ◽  
John A. Seed ◽  
Annabel Basford ◽  
Alasdair Formanuik ◽  
...  
Keyword(s):  
Quantum Chemical Calculations ◽  
Chemical Bonding ◽  
Quantum Chemical

We report the synthesis and characterisation of isostructural thorium(IV)- and uranium(IV)- silanide complexes, providing the first structurally authenticated Th-Si bond and a rare example of a molecular U-Si bond. These complexes therefore present the first opportunity to directly compare the chemical bonding of Th-Si and U-Si bonds. Quantum chemical calculations show significant and surprisingly similar 7s, 6d, and 5f orbital contributions from both actinide (An) elements in polarised covalent An-Si bonds

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