We report unambiguous experimental and theoretical evidence of intramolecular photoelectron
diffraction in the collective vibrational excitation that accompanies high-energy photoionization
of gas-phase CF4, BF3, and CH4 from the 1s orbital of the central atom. We show that the ratios
between vibrationally resolved photoionization cross sections (v-ratios) exhibit pronounced
oscillations as a function of photon energy, which is the fingerprint of electron diffraction by the
surrounding atomic centers. This interpretation is supported by the excellent agreement between
first-principles static-exchange and time-dependent density functional theory calculations and high
resolution measurements, as well as by qualitative agreement at high energies with a model in
which atomic displacements are treated to first order of perturbation theory. The latter model allows
us to rationalize the results for all the v-ratios in terms of a generalized v-ratio, which contains
information on the structure of the above three molecules and the corresponding molecular
cations. A fit of the measured v-ratios to a simple formula based on this model suggests that the
method could be used to obtain structural information of both neutral and ionic molecular species.
