Photoionization of Molecular Endohedrals.

We calculate the photoionization cross-section of a molecular endohedral M@C$_{\mathrm{N}}$. We limit ourselves to two-atomic molecules. The consideration is much more complex than for atomic endohedrals because the system even for almost spherical C$_{\mathrm{N}}$ has only cylindrical instead of spherical symmetry. But M@C$_{\mathrm{N\thinspace }}$is more interesting since the interelectron interaction in molecules is relatively stronger than in similar atoms. We present results of calculations of molecular hydrogen H$_{\mathrm{2}}$ stuffed inside almost spherical fullerene C$_{\mathrm{60}}$ -- H$_{\mathrm{2}}$@C$_{\mathrm{60}}$. For comparison, we perform calculations also for atomic endohedral He@C$_{\mathrm{60}}$. The results are obtained both in single-electron Hartree-Fock approximation and with account of multi-electron correlations in the frame of so-called random phase approximation with exchange -- RPAE. The presence of the fullerenes shell results in prominent oscillations in the endohedrals photoionization cross section. The role of interelectron correlations becomes clear by comparing HF and RPAE results for H$_{\mathrm{2}}$@C$_{\mathrm{60}}$ and He@C$_{\mathrm{60\thinspace }}$on the one side with that for H$_{\mathrm{2}}$ and He, on the other.