Absolute measurement of total electron-impact cross sections to singlet and triplet levels in helium

Absolute total apparent electron impact cross sections for excitation of helium $4{}_{}{}^1{}_{}{}^{}S$, $5{}_{}{}^1{}_{}{}^{}S$, $3{}_{}{}^1{}_{}{}^{}P$, $4{}_{}{}^1{}_{}{}^{}P$, $5{}_{}{}^1{}_{}{}^{}P$, $3{}_{}{}^1{}_{}{}^{}D$, $4{}_{}{}^1{}_{}{}^{}D$, $5{}_{}{}^1{}_{}{}^{}D$, $4{}_{}{}^3{}_{}{}^{}S$, $3{}_{}{}^3{}_{}{}^{}P$, $3{}_{}{}^3{}_{}{}^{}D$, and $4{}_{}{}^3{}_{}{}^{}D$ levels have been measured. The incident electron energies begin at 50 eV and extend to 500 eV for most levels studied and extend to 800 eV for the $3{}_{}{}^1{}_{}{}^{}P$, $4{}_{}{}^1{}_{}{}^{}S$, and $4{}_{}{}^1{}_{}{}^{}D$ levels. The $1\sigma$ errors for most of the cross sections measured are ± 10%. The important $3{}_{}{}^1{}_{}{}^{}P$ cross section is 15% below the Bethe approximation (Kim and Inokuti) at 200 eV and is within 6% of the Bethe approximation at 500 eV. The results are reported as polarization-corrected, apparent cross sections. Cascade-corrected cross sections are also given at selected energies. In addition the pressure dependencies of the apparent cross sections are presented for representative levels. Considerable attention is given to the description of the experimental apparatus, the treatment and analysis of the data, the techniques employed in absolute calibration, and the assessment of the errors in the experiment.