Symmetry selection rules for vibrationally inelastic tunneling

A combined experimental and theoretical study is presented for the C-D stre tch mode excitation of acetylene isotopes, C2HD and C2D2, on Cu(100) via in elastic electron tunneling (IET) in a scanning tunneling microscope junctio n. The calculated IET images using density functional theory show that the measured signal from C2D2 derives from the antisymmetric stretch mode. Sele ction rules are derived and involve the constraint imposed by the IET image on the symmetry characters of the vibrational mode and the adsorbate-induc ed electron states at the Fermi level.