Demonstration of Strong Forward-Backward Asymmetry in theC1sPhotoelectron Angular Distribution from Oriented CO Molecules

Angular distributions of $\mathrm{C}\left(1s\right)$ photoelectrons emitted from oriented CO molecules were measured using a new method: mass and angle-resolved photoelectron-photoion coincidence spectroscopy. Along with the angular momentum composition of the photoelectron wave, the experiment reveals pronounced forward-backward asymmetries in the photoemission intensity with respect to the molecular orientation. This asymmetry, being observed for the first time in molecular photoionization, is interpreted in terms of multiple scattering effects. Calculations using the $\mathrm{MS}-\mathrm{X}\alpha$ method show good quantitative agreement with the presented experimental results.