What is it about?
Helium is usually considered the archetype of chemical inertness. So what happens when a helium atom encounters a positively charged molecule? New computational research shows that the answer can be surprisingly simple: the electrostatic landscape of the molecular cation can predict both where helium binds and how stable the resulting complex will be.
Featured Image
Photo by Shrinath on Unsplash
Why is it important?
Helium is the second most abundant element in the universe and one of the most chemically unreactive elements known. Its reluctance to form chemical bonds makes it an ideal system for investigating the subtle forces that operate between molecules when conventional chemical bonding is not involved. In this new study published in Chemical Physics Letters, we have investigated complexes formed by helium with molecular cations, generally represented as He(M⁺). Despite their apparent simplicity, these systems can adopt different structures, depending on the molecular cation involved and on the site at which helium interacts with it. The central question is therefore straightforward: can we predict where helium will bind to a molecular cation, and can we estimate which possible structure will be the most stable? The answer emerging from the study is yes—and it can be obtained from a remarkably simple quantity: the molecular electrostatic potential (MEP). Every charged molecule generates an electric field around itself. The molecular electrostatic potential provides a way to visualize this field, identifying regions where another particle would experience different electrostatic environments. For a molecular cation M⁺, the MEP can therefore be thought of as an electrostatic map surrounding the molecule. We unequivocally report that this map contains valuable information about the interaction pathways with helium atoms. In particular, the maxima and minima of the electrostatic potential calculated on a suitable molecular surface identify regions that are associated with the preferred positions of helium.
Perspectives
Finding the possible binding positions is only part of the problem. If several isomeric He(M⁺) complexes can form, which one is more stable? Here again, the electrostatic potential provides a useful guide. The study shows that the value of the MEP at the maxima and minima associated with the different binding regions reflects the relative stability of isomeric complexes. Thus, the electrostatic map does not simply indicate where helium may interact: it also provides information about which interaction is more favorable. Although the interaction between helium and M⁺ is very different from a conventional chemical bond, the bond path and its associated critical point provide a useful framework for analyzing the electronic structure of emerging complexes. The ultimate goal is ambitious but conceptually simple: use the electrostatic potential of a molecular cation to predict where helium can bind, identify the most promising structures, and guide the discovery of previously unexplored He(M⁺) complexes. This result is important because determining the relative stability of molecular structures normally requires detailed quantum-chemical calculations for each candidate. The MEP offers a much more intuitive way of understanding the origin of these energetic differences
Dr Costantino Zazza
Universita degli Studi della Tuscia
Read the Original
This page is a summary of: Complexes of He with cationic species: The driving role of the molecular electrostatic potential, Chemical Physics Letters, November 2026, Elsevier,
DOI: 10.1016/j.cplett.2026.143017.
You can read the full text:
Contributors
The following have contributed to this page
