Crossover of Feshbach Resonances to Shape-Type Resonances in Electron-Hydrogen Atom Excitation with a Screened Coulomb Interaction

The effects of Coulomb interaction screening on electron-hydrogen atom excitation in the n = 2 threshold region are investigated by using the R-matrix method with pseudostates. The interaction screening lifts the l degeneracy of n = 2 Coulomb energy level, producing two distinct thresholds for 2s and 2p states. The phenomenon of transformation of (1,3)P and (1)D Feshbach resonances into shape-type resonances is observed when they pass across the 2s and 2p threshold, respectively, as the interaction screening increases. It is shown that this resonance transformation leads to dramatic effects in the 1s -> 2s and 1s -> 2p excitation collision strengths in the n = 2 threshold collision energy region.