Helium reaction with sodium halides under pressure

The noble gas elements are usually quite inert to chemical reactions due to the closed shell configurations. He is the most stable noble gas since its ionization energy is almost twice as large as that of Xe. It was recently demonstrated that He could react with a large number of ionic compounds with unequal number of cations and anions due to the substantial change of the electrostatic energy under high pressure. Unexpectedly, we found in the current work that He can react with NaX (X=Cl, Br, I) under high pressure also with considerable formation energy. The pressure needs to form stable NaXHe compounds decreases with increasing size of the halogen atoms. By analyzing the enthalpy components, the geometry change, and the electronic structures, we find the driving force of the He insertion reaction with AB type compound is the transformation of the structures that disproportionate the interstitial sites, making them ready to accommodate He atoms under high pressure. With the previous work, we greatly extend the reactivity of He with compounds under high pressure.