Electron-momentum-spectroscopy study on the valence electronic structure of methyl iodide: Electron correlation and relativistic effects

We report an experimental and theoretical study on the electronic structure of methyl iodide. The binding energy spectrum (BES) and electron-momentum profiles (EMPs) of valence orbitals have been measured using a high-sensitivity electron-momentum spectrometer at the impact energy of 1200 eV plus binding energy. Theoretical calculations considering the relativistic and electron correlation effects are performed to illuminate the measured results. For the two outermost orbitals, the relativistic effects are revealed by the experimental and theoretical EMPs for two spin-orbit splitting components ($2{e}_{3/2}$ and $2{e}_{1/2}$) and the C-I bonding orbital ($3{a}_{1}$). In the inner valence region, satellite structures associated with the ionizations from $2{a}_{1}$ and $1{a}_{1}$ orbitals are observed in the BES and the pole strengths for the satellites are determined by comparing the measured EMPs with the calculated ones. Moreover, distinct relativistic and electron correlation effects on the EMPs for the $2{a}_{1}$ orbital and its satellites have been found.