Wake formation in large hydrocarbon molecules

Continuum electron cusp spectra collected at 0° for ∼ MeV/ u H ⁺ and He ²⁺ projectiles on C_mH _n gases show an alteration of the cusp shape and yield for m ≥ 4 molecules. The shape of this new contribution to the cusp has a smaller width and different skew than the electron-capture-to-continuum (ECC) cusps and a yield and width dependent on projectile Z. Measurements of cusp spectra for He ⁺ projectiles (dominated by electron-loss-to-continuum processes (ELC)) show a cusp shape difference that disappears for m ≥ 4 and a normalized cusp yield that is insensitive to projectile energy. These experimental results, compared either to previous results for forward-directed continuum electron production by ECC and ELC processes or to predictions of Wake theory, are consistent only with wake production.