Low-energy electron elastic scattering and impact ionization with hydrogenlike helium in Debye plasmas

Low-energy electron elastic scattering and impact ionization with hydrogenlike helium in Debye plasmas have been investigated by employing the exterior complex scaling method. The interactions between charged particles in the plasmas have been represented by Debye-Hückel potentials. The $1s-1s$ elastic collision strengths below the $n=2$ excitation threshold of ${\mathrm{He}}^{+}$ dominated by resonance structures are calculated for different screening lengths. As the screening strength increases, the resonance peaks studied ${[}_2{{\left(1,0\right)}_2}^{+}{}^1{S}^e,{}^3{P}^o,{}^1{D}^e$, and ${}_2{{\left(0,1\right)}_2}^{+}{}^1{P}^o]$ exhibit blueshifts and then redshifts with a further increase of the screening strength, which results in dramatic changes of the collision strengths. It is found that these dynamic variation features of the resonances are related to the changes of energy levels of ${\mathrm{He}}^{+}$ in the screened potential and geometric configurations of resonances. Triple-differential-ionization cross sections in coplanar geometries at 6-Ry incident electron energy are also reported, significant changes are observed with varying screening length.

Figure 1

The $1s-1s$ elastic collision strengths below the $n=2$ excitation threshold of ${\mathrm{He}}^{+}$. The line shows the present RMPS results and the circles the present ECS results.

Figure 2

Variations of resonances ${}^1{S}^e$ and ${}^3{P}^o$ manifested in the $1s-1s$ elastic collision strengths in Debye plasmas for different screening lengths. The vertical lines indicate the excitation energies for states $2s$ and $2p$ for the specific screening length $D$.

Figure 3

Same as in Fig. 2 but for resonances ${}^1{D}^e$ and ${}^1{P}^o$.

Figure 4

Variations of the resonant positions (${}^1{S}^e, {}^3{P}^o, {}^1{D}^e$, and ${}^1{P}^o$) and the energy differences ($\mathrm{\Delta }{E}_{nl-n^{\prime }{l}^{\prime }}=E_{nl}-E_{n^{\prime }{l}^{\prime }}$ and $\mathrm{\Delta }{E}_{nl+n^{\prime }{l}^{\prime }-n^{\prime \prime }{l}^{\prime \prime }}=E_{nl}+E_{n^{\prime }{l}^{\prime }}-E_{n^{\prime \prime }{l}^{\prime \prime }}$) between levels ${\mathrm{He}}^{+}$ ($2s/2p$) and ${\mathrm{He}}^{+}$ ($1s$) in Debye plasmas for different screening lengths. The resonant positions are cited from Ref. [23] for ${}^1{S}^e, {}^1{D}^e$, and ${}^1{P}^o$ and from Ref. [15] for ${}^3{P}^o$.

Figure 5

Triple-differential cross sections of ${\mathrm{He}}^{+}$ for the incident electron energy of 6 Ry in Debye plasmas in the selected coplanar geometries. The kinetic energy of the outgoing electron and the direction of the ejected electron are (a) $E_1=0.05E$ and ${\theta }_2={15}^{\circ }$, (b) $E_1=0.95E$ and ${\theta }_2={15}^{\circ }$, (c) $E_1=0.95E$ and ${\theta }_2={150}^{\circ }$, and (d) $E_1=0.50E$ and ${\theta }_2=-{\theta }_1$, respectively; $E$ is the total energy of the whole collision system; and the ratio between $E_1/E_2$ in each panel for different screening lengths is fixed.