Multiply excited molecules in electron collisions as probed by energy and angle-resolved coincidence measurements between a scattered electron and a photon from a fragment atom

Doubly excited states of CH4 in electron collisions were investigated for the first time by measuring electron energy-loss spectra tagged with the emission of the Lyman-α photon. It turned out that the collisional cross section resulting in the emission of the Lyman-α photon originating from the doubly excited states are larger than or comparable to those originating from the nearby singly excited states and the electron interaction with molecules promotes the double excitation against the single excitation as compared with the photon interaction.