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 (photoabsorption, photoelectron and Auger) all show fine structure due to vibrational or ligand field splitting. The Si2p photoelectron and photoabsorption spectra of SiH4, SiD4 and Si2H6 show rich vibrational structure from both the symmetric and the asymmetric Si-H(D) vibrational modes. The symmetric ν1 vibrational mode dominates the photoelectron spectra of SiH4 (ν1 = 2379 cm-1) and SiD4 (ν1 = 1710 cm-1). In contrast, the asymmetric bending mode is more dominant in the photoabsorption spectra of the early Rydberg levels of SiH4 and SiD4 and completely dominant in both the photoelectron and photoabsorption spectra of Si2H6. In contrast, the core-level spectra of heavy elements such as Br and I are dominated by ligand field splitting. The high resolution Br3d photoelectron spectrum of HBr shows the 3d3/2 doublet and 3d5/2 triplet characteristic of ligand field splitting. This same splitting is shown to dominate the previously recorded MVV Auger spectrum and the pre-edge Br3d photoabsorption spectrum. (orig.)