Experimental cross sections in the extreme ultraviolet (EUV) wavelength range for the excitation of helium following electron and ${\mathrm{H}}^{+},$ ${\mathrm{H}}_2^{+},$ and ${\mathrm{H}}_3^{+}$ ion impact are presented for $\mathrm{He}\mathrm{}I$ $\mathrm{}\left(1snp\right)\mathrm{}$ ${}^1{P}^o$ states with $n=2\mathrm{}–5.$ These measurements extend over large velocity ranges 3.8–8.5 a.u. for electrons, 1.4–7.5 a.u. for protons, and 1.4–4.0 a.u. for ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$ ions, respectively, and represent the most complete data set obtained so far in the EUV. Furthermore, the methods of convergent close coupling and R matrix with pseudostates have been used here to predict excitation cross sections for the $\mathrm{He}\mathrm{}I$ $\mathrm{}\left(1snp\right)\mathrm{}$ ${}^1{P}^o$ states following electron impact and the atomic-orbital close-coupling expansion for proton impact. In particular, our theoretical results are presented and compared with our EUV experimental cross sections for equal projectile velocities together with previous experimental results, including cross sections derived from scaling procedures. The electron cross sections are found to deviate from the proton data at intermediate and lower energies $(v<\mathrm{}3.8\mathrm{}\mathrm{a}.\mathrm{u}.\mathrm{}).\mathrm{}$

• Received 26 April 2000

DOI:https://doi.org/10.1103/PhysRevA.64.012712