Electron-impact excitation of the lowest four excited states of argon

First-order many-body theory has been used to calculate the differential and integral cross sections for electron-impact excitation of the argon atom to the $4{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, $4{}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$, $4{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$, and $4{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ electronic states, for incident electron energies of 16, 20, 30, 50, and 80.4 eV. The resulting cross sections are in good agreement with recent results extracted from electron energy-loss measurements on argon. Detailed calculations show that spin-orbit coupling must be included in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ wave function in order to describe the electron-impact excitation of the state properly.