Abstract

Noble gas compounds have attracted significant research attention, mainly due to their intriguing chemical behavior under high-pressure conditions. In this paper, we identify a compound, $C2/m\text{\ensuremath{-}}{\mathrm{Xe}}_{3}{\mathrm{CO}}_{2}$, through a synergistic approach combining a particle-swarm optimization empowered structure search and first-principles calculations within a wide pressure range of 200--400 GPa, covering the pressure range of Earth's core. This compound features layered ${\mathrm{Xe}}_{6}{\mathrm{C}}_{2}{\mathrm{O}}_{4}$ sublattices, showing distinct covalent Xe-C bonds, supported by the calculated electron localization function. The presence of the covalent bonds is further corroborated by the large value of the integrated crystal orbital Hamilton population ($\ensuremath{-}4.02$ eV/pair) and the large negative Laplacian ($\ensuremath{-}4.65\phantom{\rule{0.28em}{0ex}}e/{\text{\AA{}}}^{5}$). This leads to an unusual $s{p}^{3}$-like hybridization in carbon, involving two oxygen atoms, one carbon atom, and one xenon atom. Additionally, two-phase method molecular dynamics simulations suggest that the compound exhibits liquid-state behavior at 200 GPa and 5000 K above the geotherm of the Earth's core. This shows a potential role for the compound in the liquid phase as a reservoir for the ``missing Xe'' phenomenon. Our findings not only enhance the understanding of bonding behavior in noble gas compounds, but also suggest the potential presence of ${\mathrm{Xe}}_{3}{\mathrm{CO}}_{2}$ in various astronomical objects.