He I and He II photoelectron spectra of lanthanide trichlorides in the vapour phase

Abstract

The H ei and He ll photoelectron spectra of the lanthanide trichlorides with the exception of PmCl 3 and EuC1 3 have been recorded in the vapour phase by using a pseudo-molecular beam technique. The He i spectra and the more intense part of the H en spectra of these molecules bear marked similarities to one another. These features are assigned mainly to halogen-localized ionizations. Relative intensity changes between the He i and He ii spectra imply orbital mixing between vacant metal 5d orbitals and ligand-localized valence molecular orbitals. Weak features observed primarily in the H en spectra are believed to be due to 4f -1 ionization and appear to support the atomic nature of the 4f shell. These features indicate that the 4f _1 partial ionization cross section falls rapidly across the lanthanide series. The metal-localized 5p_1 ionization has been identified in some lighter members of the group and the He i and H en spectra of EuC1 2 and N dl 3 are also reported.