Characteristic low-energy electrons emitted in proton-atom collisions at intermediate impact velocities

We report experimental and theoretical electron spectra within the very low-electron-energy range below 30 eV. Doubly differential cross sections for ionization of different noble gases (He, Ne, Ar, Kr, Xe) by impact of 100-keV and 225-keV protons are reported. A pronounced structure in the low-energy region of emitted-electron spectra is observed with different intensities for the different targets. We compare our experimental findings with two theoretical models: the first-order Born approximation and the “continuum-distorted-wave–eikonal-initial-state” model using different optimized central potentials to calculate the bound and continuum states of the target. We attribute our experimental observation to a signature of the predicted low-energy binary peak.