Theoretical study of valence photoelectron spectra of Re(CO)5X (X=Cl, Br, and I): a spin-orbit DK3 symmetry-adapted cluster/symmetry-adapted cluster-configuration interaction study

The valence photoelectron spectra of Re(CO)(5)X (X=Cl, Br, and I) are studied theoretically using symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theory. The relativistic effects are included by the third-order Douglas-Kroll (DK3) method, and the spin-orbit coupling is also considered. Both electron correlation and relativistic effects are significant in assigning the valence photoelectron spectra of Re(CO)(5)X (X=Cl, Br, and I). DK3-SAC/SAC-CI provides values for the relative peak positions in a reasonable agreement with the observed photoelectron spectra. The sequence of ionization energies for Re(CO)(5)Cl, Re(CO)(5)Br, and Re(CO)(5)I are calculated as e(')a(1)(Cl)]>e(')e(Re+Cl)] approximately e(")e(Re+Cl)]>e(")b(2)(Re)]>e(')e(Re-Cl)]>e(")e(Re-Cl)], e(')a(1)(Br)]>e(')e(Re+Br)]>e(")e(Re+Br)+b(2)(Re)]>e(")b(2)(Re)+e(Re+Br)]>e(')e(Re-Br)]>e(")e(Re-Br)], and e(')e(Re+I)+a(1)(I)]>e(")b(2)(Re)+e(Re+I)] approximately e(')a(1)(I)+e(Re+I)]>e(")e(Re+I)+b(2)(Re)]>e(')e(Re-I)]>e(")e(Re-I)], respectively. These assignments are quite new and different from previous assignments.