A new spin-averaged potential energy surface (PES) for non-reactive O2(Σg−3) + O2(Σg−3) collisions is presented. The potential is formulated analytically according to the nature of the principal interaction components, with the main van der Waals contribution described through the improved Lennard-Jones model. All the parameters involved in the formulation, having a physical meaning, have been modulated in restricted variation ranges, exploiting a combined analysis of experimental and ab initio reference data. The new PES is shown to be able to reproduce a wealth of different physical properties, ranging from the second virial coefficients to transport properties (shear viscosity and thermal conductivity) and rate coefficients for inelastic scattering collisions. Rate coefficients for the vibrational inelastic processes of O2, including both vibration-to-vibration (V–V) and vibration-to-translation/rotation (V–T/R) energy exchanges, were then calculated on this PES using a mixed quantum–classical method. The effective formulation of the potential and its combination with an efficient, yet accurate, nuclear dynamics treatment allowed for the determination of a large database of V–V and V–T/R energy transfer rate coefficients in a wide temperature range.
Resonance-assisted hydrogen bonds (RAHB) are intramolecular contacts that are characterised by being particularly energetic. This fact is often attributed to the delocalisation of π electrons in the system. In the present article, we assess this thesis via the examination of the effect of electron-withdrawing and electron-donating groups, namely −F, −Cl, −Br, −CF3, −N(CH3)2, −OCH3, −NHCOCH3 on the strength of the RAHB in malondialdehyde by using the Quantum Theory of Atoms in Molecules (QTAIM) and the Interacting Quantum Atoms (IQA) analyses. We show that the influence of the investigated substituents on the strength of the investigated RAHBs depends largely on its position within the π skeleton. We also examine the relationship between the formation energy of the RAHB and the hydrogen bond interaction energy as defined by the IQA method of wave function analysis. We demonstrate that these substituents can have different effects on the formation and interaction energies, casting doubts regarding the use of different parameters as indicators of the RAHB formation energies. Finally, we also demonstrate how the energy density can offer an estimation of the IQA interaction energy, and therefore of the HB strength, at a reduced computational cost for these important interactions. We expected that the results reported herein will provide a valuable understanding in the assessment of the energetics of RAHB and other intramolecular interactions.
Silver(I) coordination compounds display an interesting geometrical diversity, the possibility of having distinct coordination numbers (typically from 2 to 4) and the capability of forming argentophilic (Ag⋅⋅⋅Ag) interactions. These properties complicate the accurate prediction of structures of silver complexes under certain experimental conditions. In this work, we show how subtle modifications in thiolate and phosphine ligands exert important effects on the nuclearity and geometry of phosphine caped clusters [Ag(SR)]n (n=4, 6 and 8). We rationalize these effects in terms of the electronic environment of silver centers by analyzing the electronic density of the single‐crystal X‐ray structures via the Quantum Theory of Atoms in Molecules (QTAIM) and the Non‐Covalent Interaction (NCI)‐Index. Furthermore, we characterized attractive and repulsive argentophilic contacts by means of the Interacting Quantum Atoms (IQA) energy partition. Our results provide insights on the effects of ancillary ligands in controlling the structure of silver‐thiolate clusters. Such control is relevant towards a bottom‐up approach to the atomic precise construction of higher nuclearity clusters.
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