Confirmation of 9Σg− and 8Σu− ground states of Fe2 and Fe2− by CASSCF/MRCI

The ground states of Fe2 and Fe2− are assigned to 9Σ−g and 8Σ−u, respectively, with re=219 and 227 pm and ωe=303 and 255 cm−1, respectively. The corresponding configurations 3d134s3 and 3d134s4 are those suggested for the respective ground states by Leopold et al. [J. Chem. Phys. 88 (1988) 3780] but ignored in all previous computational studies including two most recent density functional studies on first row transition metal dimers. The two bands of the photoelectron spectrum of Fe2− are assigned to the 9Σg− and 7Σg− states of Fe2 with an energy difference of 0.48 eV.