A HD-like (HD: mono-deuterated hydrogen molecule) isotopic dipole moment is proposed as a sensible probe for molecular environments, in particular for electrostatic fields and polarizable (reactive) sites of molecules. Fictitious nuclear masses are chosen in order to yield a rigid dipole with a small appropriate magnitude. Upon subtracting the Born-Oppenheimer energy, the interaction is reduced to field-dipole-like and dipolepolarizability-like terms, the last one being particularly informative since connected to potentially reactive sites. Possible asymmetries of this term appear as signatures of charged sites in the molecule. The field strength and orientation are easily obtained by identifying the minimum field-dipole energy configuration and flipping the dipole from it. Tests with hydrogen, water, benzene, and chlorobenzene molecules confirm the good performance of the method. In an application to test the present models for hydrogen activation by a frustrated Lewis pair, the full potential of the method is assessed.isotopic ficticious probe, molecular environment, molecular interactions, post Born-Oppenheimer 1 | INTRODUCTION In the last decades, the applicability of ab initio quantum chemical methods has been extended to the study of structural and dynamical properties of very large isolated molecules. Many important processes of modern science however, including those involving life, demand a step further, namely the generation of accurate theoretical knowledge of the properties of molecular environments, which are connected to the detailed description of general molecular interactions, van der Waals (vdW) and other, and the identification of reactive sites for chemical processes. [1,2] The quite important topics of biological recognition, [3] hydrogen bonding, [4] and computer simulations and modeling of molecular complexes and new materials, [5][6][7] for instance, lie on this subject. Particularly, the electrostatic field created by a source molecule on its surroundings is considered as being helpful for this prospect, [5,[8][9][10][11][12] since it indicates how the molecule affects statically its environment. But the knowledge of the molecular polarization "potential," meaning the way the molecule would react dynamically to the presence of another, is of even greater importance. [13] Reporting back to a review by Scrocco and Tomasi, [14] many investigations in these fields in the last decades rely on the molecular electrostatic potential (MEP) method, in order to investigate structure, reactivity, and other properties of large molecules. Ab initio MEP derives directly from the electronic density [8,9,13] and is the only method of general applicability so far. On the other hand, being static properties of isolated molecules, MEP fields can give an inaccurate description of the intermolecular interactions in regions close to the source molecule. This unsatisfactory situation motivated recent movements to the point charges model [15] and from the last to particular multipole expansions [16] and fragmente...
The Si+SO2 reaction is investigated to verify its impact on the abundances of molecules with astrochemical interest, such as SiS, SiO, SO and others. According to our results Si(3P) and SO2 react barrierlessly yielding only the monoxides SO and SiO as products. No favourable pathway has been found leading to other products, and this reaction should not contribute to SiS abundance. Furthermore, it is predicted that SiS is stable in collisions with O2, and that S(3P)+SiO2 and O(3P)+OSiS will also produce SO+SiO. Using these results and gathering further experimental and computational data from the literature, we provide an extended network of neutral-neutral reactions involving Si- and S-bearing molecules. The effects of these reactions were examined in a protostellar shock model, using the Nautilus gas-grain code. This consisted in simulating the physicochemical conditions of a shocked gas evolving from (i primeval cold core, (ii the shock region itself, (iii and finally the gas bulk conditions after the passage of the shock. Emphasising on the cloud ages and including systematically these chemical reactions, we found that [SiS/H2] can be of the order of ∼ 10−8 in shocks that evolves from clouds of t = 1 × 106 yr, whose values are mostly affected by the SiS+O $\longrightarrow$SiO+S reaction. Perspectives on further models along with observations are discussed in the context of sources harbouring molecular outflows.
π‐ and σ‐holes are nonnuclear molecular regions of positive electric potential, which make non‐covalent interactions with negative sites, for example, lone pairs of molecules containing nitrogen or oxygen, the so called π‐ and σ‐hole bonds. We investigate these bonds locally using a probe programmed as a virtual molecule. Unlike the hydrogen bond, electric fields are detected having strengths that are different from the sum of the separated parts, meaning that molecular electrostatic potential surfaces analysis of the different parts are not enough to analyze the bonds. Based on an application of the Hellmann‐Feynman theorem, which states that intermolecular bonds are fully described by Coulombian interactions (electrostatic plus polarization), we connect the electric field strength with the bond strength measured in experiments, so that it can be considered as a quantifier for the bonds.
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