Ab-initio calculation of the C1s photoelectron spectrum of C2H2

The C1s photoelectron spectrum of C2H2, measured by Kempgens et al. [Phys. Rev. Lett. 79, 3617 (1997)] and characterized by the presence of a core-level splitting, has been calculated and interpreted using an ab initio quantum-mechanical method that allows detailed analysis of photoionization processes and accurate reproduction of spectral profiles. The anisotropy of the electron emission, measured in a hypothetical experiment in which the orientation of the molecules can be established, has been also predicted and analyzed.