Penning ionization electron spectra of half-sandwich metal complex compounds ((η 6 -C 6 H 6 )Cr(CO) 3 and (η 5 -C 5 H 5 )Mn(CO) 3 ) by collision with He * (2 3 S) metastable atoms were observed. With collision-energy/electron-energy-resolved measurement of ejected electrons, information on anisotropic interaction potential energy for the spatial region where the corresponding MO extends were investigated by measuring collision energy dependence of partial ionization cross-sections (CEDPICS) for each ionic state. Assignments of ionic states are also discussed on basis of orbital reactivity of Penning ionization, slope of CEDPICS, and an orbital energy calculation by density functional theory. Since similarity between an excited He * (2 3 S) atom and a ground state Li atom is known in interaction with targets, quantum chemical calculations for intramolecular interactions with a Li(2 2 S) atom are also performed. Large reactivity and strong attractive interactions are observed around oxygen atoms of carbonyl groups. On the other hand, repulsive or weak attractive interactions are also found for the benzene and cyclopentadienyl rings.