Pure rotational excitation ofH2at electron impact energies of 3 to 100 eV

Cross sections for pure rotational excitation ($J=1\mathrm{}\to 3$) in ${\mathrm{H}}_2$ are reported at electron energies $E_0$ of 15 eV to 100 eV at scattering angles $\theta$ of 115°, 3 to 40 eV at 20°, and at 40 eV at angles between 10° and 135°. It is found that for intermediate $E_0$ the probability of pure rotational excitation at high $\theta$ is greater than that for elastic scattering. Moreover, this probability is found to decrease slowly with $E_0$, having a value at its peak (at 4 eV) which is only ∼ 20 times that at 100 eV.