Editing Selection rule (section)

=== Surface ===
In [[vibrational spectroscopy|surface vibrational spectroscopy]], the ''surface selection rule'' is applied to identify the peaks observed in vibrational spectra. When a [[molecule]] is [[adsorption|adsorbed]] on a substrate, the molecule induces opposite image charges in the substrate. The [[dipole|dipole moment]] of the molecule and the image charges perpendicular to the surface reinforce each other. In contrast, the dipole moments of the molecule and the image charges parallel to the surface cancel out. Therefore, only molecular vibrational peaks giving rise to a dynamic dipole moment perpendicular to the surface will be observed in the vibrational spectrum.