Rotational Excitation of the HD Molecule by Low-Energy Electron Collision

The rotational excitation of HD by low-energy electron collision is discussed for the first time. In the thermal-energy region, the Born approximation is used to derive relevant cross sections semi-quantitatively. In the eV-region, the adiabatic approximation is used to discuss the problem qualitatively. It is found that except in the neighborhood of the threshold energy, the rotational excitation cross section σ( J → J +2), J being the rotational quantum number of the molecule, does not change much when H 2 is replaced by HD. For HD, transitions with odd Δ J are also allowed. However, the cross sections for these transitions are found to be fairly small. The momentum-transfer and the rotational stopping cross sections are discussed. Excitation of D 2 is also considered for comparison.