  We have studied the Stark effect in the soft x-ray region for various small
molecules by calculating the field-dependent x-ray absorption spectra. This
effect is explained in terms of the response of molecular orbitals (core and
valence), the molecular dipole moment, and the molecular geometry to the
applied electric field. A number of consistent trends are observed linking the
computed shifts in absorption energies and intensities with specific features
of the molecular electronic structure. We find that both the virtual molecular
orbitals (valence and/or Rydberg) as well as the core orbitals contribute to
observed trends in a complementary fashion. This initial study highlights the
potential impact of x-ray Stark spectroscopy as a tool to study electronic
structure and environmental perturbations at a sub-molecular scale.
