Multilayers of fullerenes with and without endohedral Ar units, ${\mathrm{Ar@C}}_{60}$ and ${\mathrm{C}}_{60}$, were investigated by photoemission and density-functional theory. The stoichiometry and the endohedral nature of Ar were checked by x-ray photoelectron spectroscopy and x-ray photoelectron diffraction. Valence-band ultraviolet photoemission spectra showed a strong hybridization of the Ar $3$$p$ valence shell with the $6$$T_{1u}$ molecular orbital of ${\mathrm{C}}_{60}$. A hybridization gap of $1.6$ $\pm$ $0.2$ eV was found. This is in agreement with density-functional theory, which predicts $1.47$ eV and indicates that ${\mathrm{Ar@C}}_{60}$ is a noble gas compound with a strong coupling between Ar and the ${\mathrm{C}}_{60}$ cage. No giant Ar photoemission cross section as previously predicted for the gas phase in Phys. Rev. Lett. 99 243003 (2007) was found.

• Received 1 July 2010

DOI:https://doi.org/10.1103/PhysRevA.82.051201