Electrical anharmonicity in hydrogen bonded systems: complete interpretation of the IR spectra of the Cl-H[combining right harpoon above] stretching band in the gaseous (CH3)2OHCl complex

Breaking the Structure of Liquid Hydrogenated Alcohols Using Perfluorinated tert-Butanol: A Multitechnique Approach (Infrared, Raman, and X-ray Scattering) Analyzed by DFT and Molecular Dynamics Calculations

The state of aggregation at room temperature of tert-butanol (TBH) and perfluoro tert-butanol (TBF) liquid mixtures is assessed by vibrational spectroscopy (Raman and infrared) and X-ray diffraction and analyzed using density functional theory (DFT) and molecular dynamics (MD) simulations. It is shown that larger clusters (mostly tetramers) of TBH are destroyed upon dilution with TBF. Small oligomers, monomers, and mainly heterodimers are present at the equimolar concentration. At variance with slightly interacting solvents, the signature of hetero-oligomers is shown by the appearance of a new broad band detected in the infrared region. The same spectral observation is detected for mixtures of other hydrogenated alcohols (methanol and 1-butanol). The new infrared feature is unaffected by dilution in a polar solvent (CDCl₃) in a high-concentration domain, allowing us to assign it to the signature of small hetero-oligomers. MD simulations are used to assess the nature of the species present in the mixture (monomers and small hetero-oligomers) and to follow the evolution of their population upon the dilution. Combining MD simulations with DFT calculations, the infrared spectral profile is successfully analyzed in equimolecular mixtures. This study shows that TBF is a structure breaker of hydrogen-bonded alcohol networks and that the TBF (donor)-TBH (acceptor) heterodimer is the dominant species in an extended range of concentration, centered in the vicinity of the equimolar fraction.

Dynamics & Spectroscopy with Neutrons-Recent Developments & Emerging Opportunities

This work provides an up-to-date overview of recent developments in neutron spectroscopic techniques and associated computational tools to interrogate the structural properties and dynamical behavior of complex and disordered materials, with a focus on those of a soft and polymeric nature. These have and continue to pave the way for new scientific opportunities simply thought unthinkable not so long ago, and have particularly benefited from advances in high-resolution, broadband techniques spanning energy transfers from the meV to the eV. Topical areas include the identification and robust assignment of low-energy modes underpinning functionality in soft solids and supramolecular frameworks, or the quantification in the laboratory of hitherto unexplored nuclear quantum effects dictating thermodynamic properties. In addition to novel classes of materials, we also discuss recent discoveries around water and its phase diagram, which continue to surprise us. All throughout, emphasis is placed on linking these ongoing and exciting experimental and computational developments to specific scientific questions in the context of the discovery of new materials for sustainable technologies.

How far the vibrational exciton interactions are responsible for the generation of the infrared spectra of oxindole crystals?

Oxindole (indolin-2-one, Ox) is a unique and a crucial molecular system in spectroscopic studies. Indole is the core structure of many substances found in the human body (tryptophan, serotonin) and the indole alkaloids have highly differentiated pharmacological properties such as analgesic, anti-fever and anti-inflammatory. The Ox's structural results given in the Cambridge Structural Database revealed the existence of only one crystalline form of Ox, referred to the α-form. However, we have experimentally noticed the existence of two polymorphic forms during the crystallization of Ox. Furthermore, the significant spectral differences that we have observed in the solid state infrared spectra of these two forms additionally confirm the existence of the polymorphism phenomenon. Of the four polymorphic forms of Ox, two of them - α - and β-forms - were of particular interest. In the crystalline lattices of both polymorphs, we observed a similar pattern of molecular arrangements giving rise to the supramolecular synthon according to the terminology of Etter. Moreover, hydrogen bonds in the dimer of the α-form are found to be non-equivalent (non-centrosymmetric dimers), having a length of 2797 Å and 2979 Å, respectively. Comparatively, in the most densely packed crystalline structure of Ox, the β-form, the dimer is formed by a pair of almost identical intermolecular hydrogen bonds and consequently the crystals of β-form exhibited spectral properties typical to centrosymmetric hydrogen bond dimers. In addition, the spectroscopic studies that we have conducted to polymorphic forms of Ox, isotopically diluted with deuterium, show the dramatic influence of isotopic substitution in the hydrogen bridge on the infrared spectra of hydrogen bonding. Thus, the main goal of this work is the proposition of a theoretical approach that can describe the main features of the crystalline infrared spectra of the Ox polymorphs. The proposed approach is based on the phenomenon of the exciton coupling results directly from intermolecular interactions in the vibrationally excited state which leads to the delocalization of the excitation over the molecules in the lattice and to the Davydov splitting effect in the crystalline spectra.