Electron-impact excitation of the 3 Pi u-(v=0,1,2,3; N=1) states of H2: Cross sections and anisotropy parameters.

Abstract

We have applied the density-matrix formalism and a distorted-wave approximation scheme to calculate Stokes parameters, polarization fractions, alignment tensors, and orientation vectors for the $^{3}\mathrm{\ensuremath{\Pi}}_{\mathrm{u}}^{\mathrm{\ensuremath{-}}}$(v=0,1,2,3; N=1) states of ${\mathrm{H}}_{2}$, as well as rovibrationally resolved state-to-state differential and integral cross sections for the $^{1}\mathrm{tsum}_{\mathrm{g}}^{+}$(v=0)\ensuremath{\rightarrow}d $^{3}\mathrm{\ensuremath{\Pi}}_{\mathrm{u}}^{\mathrm{\ensuremath{-}}}$(v=0,1,2,3) excitation by electron impact at incident energies ranging from 15 to 40 eV. This is a systematic study for ${\mathrm{H}}_{2}$ of these quantities as a function of incident energy and final vibrational levels. Good agreement between our calculated Stokes parameters and the only available experimental data is observed. Our results show that these parameters are nearly independent of the vibrational quantum number of the excited state, that the polarization of the radiation emitted by the target in the subsequent decay process increases with increasing incident energies, and that the Stokes parameters are small compared with atomic values even if the fine and hyperfine structure effects are not taken into account.