Theoretical study of the electronic structure and photoelectron spectra of Ni(CO)4, Co(CO)3NO, Fe(CO)2(NO)2, MnCO(NO)3 and Cr(NO)4

The electronic structure and ionization energies of the first transition series of isoelectronic carbonyl nitrosyls were studied using ab initio 2h-1p configuration interaction (CI) and local density calculations. A 2h-1p CI scheme is found to be fairly successful except for Fe(CO)2(NO)2 and notably superior to DSCF calculations. Excellent results are afforded by the local density approach based on the Xalpha potential. A detailed analysis of higher excitation levels in selected orbital spaces was performed on Fe(CO)2(NO)2, showing the importance of quasi degenerate correlation effects up to 4h-3p excitations.