Multiconfiguration self-consistent-field ab initio and local-density-functional studies on the vibrational structure of core-level photoelectron spectra of ${\mathrm{SiH}}_4$ and ${\mathrm{GeH}}_4$

The periodic trends in the vibrational structure of core-level photoelectron spectra are studied by multiconfiguration self-consistent-field ab initio and local-density-functional calculations on ${\mathrm{SiH}}_4$ and ${\mathrm{GeH}}_4$. Contributions from both symmetric stretching and bending vibrations to the vibrational structure are studied. These periodic trends are rationalized by the screening of the core charge, and in terms of electrostatic and relaxation contributions to core ionization, which determine the change in the M-H (M=Si,Ge) bond length.