Abstract The He (I) and He (II) photoelectron spectra are reported for (η 5-C 5 H 5) MX 3 (M= Ti, Zr, Hf; X= Cl, Br) and some methylcyclopentadienyl and pentamethylcyclopentadienyl derivatives. Unambiguous assignments are made of the Cp orbitals, the halide a 2 and e orbitals. Very regular trends are observed in the ionization energies upon substitution of the ring, metals and ligands.
