Outer valence ionic states of Cr(CO)₆ and (η⁵- C₅H₅)Co(CO)₂ observed by two-dimensional penning ionization electron spectroscopy

Outer valence ionic states of Cr(CO)₆ and (η⁵- C₅H₅)Co(CO)₂ were investigated by means of Penning ionization electron spectroscopy (PIES) upon collision with metastable He^*(2³S) excited atoms as well as high-level ab initio molecular orbital calculations taking electron correlation effects into consideration. By the 2D measurement combining the collision-energy-resolved technique of the metastable atomic beam and electron spectroscopy, ionic-state-resolved measurement of collision energy dependence of partial ionization cross sections (CEDPICS) was carried out. Because partial Penning ionization cross sections can be connected to the spatial extent of corresponding molecular orbitais (MOs) outside the boundary surface of colliding He^* atoms, different slopes of CEDPICS were related to anisotropic interaction around the MO region. The observed CEDPICS and PIES band intensity were consistent with the order of calculated ionic states.