Excitation ofP3(2p)2state of helium by electron impact

Close-coupling cross sections for the electron-impact parity-unfavored transition ${}_{}{}^3{}_{}{}^{}P{\left(2\mathrm{}p\right)}^2\leftarrow {}_{}{}^1{}_{}{}^{}S{\left(1\mathrm{}s\right)}^2$ in helium are calculated in an integral equation approach. At an energy 0.11 eV above threshold the present formalism yields a cross section of $1.55\times {10}^{-4\mathrm{}}{a}_0^2$ which is in good agreement with experiment. Our calculated slope at this energy is 6 × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$/eV against an experimental value of 4 × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$/eV. The present cross sections satisfy the threshold law for parity-unfavored transitions. A Born-Oppenheimer (BO) calculation is also performed, and it is found that near threshold BO cross sections are too small in comparison with experimental results. The dependence of BO cross sections on the choice of atomic wave functions is also examined.