HeI and HeII Photoelectron Spectra of Lanthanide Trichlorides in the Vapour Phase

The HeI and HeII photoelectron spectra of the lanthanide trichlorides with the exception of PmCl_3 and EuCl_3 have been recorded in the vapour phase by using a pseudo-molecular beam technique. The HeI spectra and the more intense part of the HeII spectra of these molecules bear marked similarities to one another. These features are assigned mainly to halogen-localized ionizations. Relative intensity changes between the HeI and HeII spectra imply orbital mixing between vacant metal 5d orbitals and ligand-localized valence molecular orbitals. Weak features observed primarily in the HeII 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 HeI and HeII spectra of EuCl_2 and NdI_3 are also reported.