中文摘要：

Electron momentum spectroscopy （EMS） has been used for the first time to study core electronic structure of iso- C2H2C12. In the present work, the pronounced difference between ionization energies of two Cls core orbitals （2Al and 3A1 ） is seen as a chemical shift of 3 eV, which is due to different chemical environments of the related carbon atoms. Both the calculated spherically averaged core electron momentum distributions （MDs） and three-dimensional electron momen- tum density maps show that these core molecular orbitals （MOs） 2AI and 3AI exhibit strong atomic orbital characteristics in real and momentum space. However, the core states 2B2 and 4AI, which are almost degenerate and related to two equiv- alent atoms, exhibit notable differences between the momentum and position depictions. In contrast to the position space, the momentum density maps of these two core MOs highlight the interference effects which are due to the nuclear positions. The 2B2 orbital of iso-C2H2C12 is the antisymmetric counterpart of the 4Ai core orbital in real space. However, it relates to the 4AI orbital by an exchange of maxima and minima in momentum space. Due to interference effects between electrons scattered from different atomic centers, modulations with a periodicity of 1.12 a.u. can be seen in the computed momentum densities, which tend to decay with increasing electron momenta. Accordingly, the EMS can not only effectively image the electronic structure of compounds by studying valence orbitals, but also provides direct information on the nature of the nuclear geometry by investigating the core states.