VIBRATIONAL AND LIGAND-FIELD EFFECTS IN THE HIGH-RESOLUTION CORE-LEVEL SPECTROSCOPY OF MOLECULES

High resolution Si2p and Br3d core-level spectra of small molecules (p hotoabsorption, photoelectron and Auger) all show fine structure due t o vibrational or ligand field splitting. The Si2p photoelectron and ph otoabsorption spectra of SiH4, SiD4 and Si2H6 show rich vibrational st ructure from both the symmetric and the asymmetric Si-H(D) vibrational modes. The symmetric nu1 vibrational mode dominates the photoelectron spectra of SiH4 (nu1 = 2379 cm-1) and SiD4 (nu1 = 1710 cm-1). In cont rast, the asymmetric bending mode is more dominant in the photoabsorpt ion spectra of the early Rydberg levels of SiH4 and SiD4 and completel y dominant in both the photoelectron and photoabsorption spectra of Si 2H6. In contrast, the core-level spectra of heavy elements such as Br and I are dominated by ligand field splitting. The high resolution Br3 d photoelectron spectrum of HBr shows the 3d3/2 doublet and 3d5/2 trip let characteristic of ligand field splitting. This same splitting is s hown to dominate the previously recorded MVV Auger spectrum and the pr e-edge Br3d photoabsorption spectrum.