  We study the significance and characteristics of interfacial dynamical charge
transfer at metal-organic interfaces for the organic semiconductor model system
1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) on Ag(111)
quantitatively. We combine infrared absorption spectroscopy and
dispersion-corrected density functional theory calculations to analyze dynamic
dipole moments and electron-vibron coupling at the interface. We demonstrate
that interfacial dynamical charge transfer is the dominant cause of infrared
activity in these systems and that it correlates with results from partial
charge and density of states analysis. Nuclear motion generates an additional
dynamic dipole moment but represents a minor effect except for modes with
significant out-of-plane amplitudes.
