Double-slit experiment with a polyatomic molecule: vibrationally resolved C 1s photoelectron spectra of acetylene

We report the first evidence for double-slit interferences in a polyatomic molecule, which we have observed in the experimental carbon 1s photoelectron spectra of acetylene (or ethyne). The spectra have been measured over the photon energy range of 310-930eV and show prominent oscillations in the intensity ratios g()/ u() for the vibrational quantum numbers = 0,1 and for the ratios s( = 1)/ s( = 0) for the symmetry s = g,u. The experimental findings are in very good agreement with ab initio density