Reflective and collateral photoionization of an atom inside a fullerene: Confinement geometry from reciprocal spectra

In the photoionization of an atom endohedrally confined in a fullerene the electrons directly ionized from the atom partially reflect from the cage. However, the valence atomic electrons can also eject from the cage collaterally with their direct emission. The reflective and the collateral amplitudes oscillate in the electron's momentum space with frequencies determined by their path differences from the direct amplitude. Resulting cross sections reveal the confining geometry in the Fourier conjugate domain. The frequency pattern distinguishes the atomic emission from the fullerene emission.