PES of higher temperature vapors: Lithium halide monomers and dimers

The He (I) photoelectron spectra of ''pure'' monomers and dimers of the lithium halides have been obtained by using a double-oven technique to vary the dimer:monomer ratio. The lithium halide monomer spectra conform nicely to a model based on spin--orbit and ligand field interactions previously introduced. The first ionization potentials of the dimers are in each case higher than in the corresponding monomers. These conclusions are also deduced in this paper by ionic model calculations and molecular calculations of the X-α type, using the discrete variational method. The X-α calculations enable us to assign tentatively the dimer valence bands. These calculations have been extended to trimer and tetramer structures and indicate an oscillation in the first ionization potential in the series encompassing monomer through tetramer. Some experimental verification exists up to trimer. The oscillatory behavior is also obtained in a crude ionic model calculation. An experimental method using photoionization mass spectrometry is suggested for the study of larger clusters and is tested for Na2I2