Theoretical study of valence photoelectron spectrum of OsO4: A spin-orbit RESC-CASPT2 study

Abstract

The valence photoelectron spectrum (bands from A to E) of OsO4 is studied by second-order complete active space perturbation theory (CASPT2). The relativistic effects are included by the relativistic elimination of the small components (RESC) scheme. Spin-orbit coupling is also considered. Both the electron correlation and relativistic effects are significant on the peak position and intensity of valence photoelectron spectrum of OsO4. RESC-CASPT2 gives values for the peak position and intensity in reasonable agreement with the resolved photoelectron spectrum data. The state ordering is predicted as T12(1t1)>2T2(3t2)>2A1(2a1)>2T2(2t2)>2E2(1e). Electron correlation shifts all peak positions by 2.5–3.5 eV to the high-energy side. Spin-free relativistic effects shift the band D by 0.8 eV again to the high-energy side due to the stabilization of Os 6s orbital. The present study confirms that the band C arises from the spin-orbit coupling in the ionic T22(3t2) state. Under the E band, there are many two-electron shake-up peaks in addition to the two one-electron ionization peaks. The broad feature of the E band is due to the satellite peaks and can be well explained through the introduction of the relativistic effects.