The effects of Coulomb interaction screening on electron–hydrogen-atom elastic and excitation scattering around the $n=2$ threshold have been investigated by using the $R$-matrix method with pseudostates. The elastic and excitation collision strengths show dramatic changes when the interaction screening length $D$ varies from $\infty$ to 3.8 a.u., as a result of the convergence of ${}^{1,3}S$ Feshbach resonances to the varying 2$s$ threshold and of the transformation of ${}^{1,3}P$ and ${}^{1}D$ Feshbach resonances into shape-type resonances when they pass across the 2$s$ and 2$p$ threshold at certain critical value of $D$, respectively [S. B. Zhang et al., Phys. Rev. Lett. 104, 023203 (2010)]. The resonance parameters for a large number of $D$ in the range $D=\infty$–3.8 a.u. are presented. It is observed that the ${}^{1,3}P$ and ${}^{1}D$ resonance contributions to the elastic and excitation collision strengths decrease rapidly with decreasing $D$ after the resonance passes the critical $D$ value. The contribution of a ${}^1{S}^e$ Feshbach resonance to the elastic or excitation collision strength changes into a cusp after the resonance merges into its parent 2$s$ state and immerses into the background with the further decrease of $D$.

• Received 15 January 2010

DOI:https://doi.org/10.1103/PhysRevA.81.032707