Electron diffraction with bound electrons: The structure sensitivity of Rydberg Fingerprint Spectroscopy

Rydberg Fingerprint Spectroscopy (RFS) has proven to be a powerful method to probe molecular structures, especially transient structures with large amounts of internal energy. The technique is related to electron diffraction in that the molecular structure sensitivity originates from the wavefunction phase shift of the probe electron induced by the charge distributions in the molecule. Exploiting the close relationship between the two techniques, we investigate the origin of the molecular structure sensitivity of RFS by introducing a molecular ion core model that is solved analytically using perturbation theory as well as numerically using a numerical-grid method. The dependence of the Rydberg electron energy on some molecular parameters is investigated and the effectiveness of the numerical-grid method in solving our one-electron Schrödinger equation is validated. A reasonable consistency between experimental and computed quantum defect values is shown for specific molecular ion core model parameters.