Spectroscopic evidence of a Xe-Xe bond in the linear Xe₂Au⁺Xe ion

The closed-shell nature of Xe atoms precludes the formation of Xe-Xe bonds other than based on van der Waals interactions. Here, we present experimental evidence showing that the complexation of Xe atoms to a Au⁺ ion leads to stabilization of a Xe-Xe interaction going beyond purely dispersive. Infrared spectroscopy is used to identify the geometry of AuXe₃⁺ as a linear structure in which two Xe atoms form a direct bond, instead of an expected geometry in which three Xe atoms coordinate directly with a central Au⁺ ion. Density functional theory and coupled-cluster calculations show that this bond possesses an enhanced orbital mixture, in comparison to that in the isolated Xe₂ dimer. The calculations are validated by observed vibrational modes at 134 and 163 cm^-1 for AuXe₃⁺, and a AuXe₂⁺-Xe bond energy of 0.04 ± 0.01 eV estimated from the temperature-dependent formation.