A distorted-wave Born-approximation method has been used to obtain various results for the electron- and positron-impact excitations of the helium atom initially from its ground (1 ${}_{}{}^1{}_{}{}^{})$ and excited metastable (2 ${}_{}{}^1{}_{}{}^{})$ states to 2 ${}_{}{}^1{}_{}{}^{}P$, 3 ${}_{}{}^1{}_{}{}^{}S$, and 3 ${}_{}{}^1{}_{}{}^{}P$ states. The results are obtained for differential and integrated cross sections. For the 2 ${}_{}{}^1{}_{}{}^{}P$ and 3 ${}_{}{}^1{}_{}{}^{}P$ excitations, coincidence parameters λ and χ as well as the circular polarization $P_3$ are also reported. The correlation effect of the target electrons for the 1 ${}_{}{}^1{}_{}{}^{}$S(2 ${}_{}{}^1{}_{}{}^{}$S)→$2^1$P transition is also considered. Our various results are compared with available previous theoretical and experimental results.

• Received 31 May 1988

DOI:https://doi.org/10.1103/PhysRevA.38.2767