Rotational Excitation of Diatomic Molecular Systems. II. H2+

Rotational excitation cross sections of H ₂ ⁺ by electron impact are evaluated in the adiabatic approximation from phase-shifts of previous papers based on the method of single center polarized orbitals. In consonance with classically averaged fixed-nuclei cross sections of the previous papers, we find here that the quantitative changes due to polarization and permanent distortion on rotational excitation are also small. However the relative sizes of these two effects are interchanged with permanent distortion here being more important; the reasons for this are easily seen. In the first part of the paper, generalizations of the formulae of the adiabatic theory for a charged molecular target (molecular ion) are given. It is concluded in that case that the adiabatic theory can be made to be accurate down to an energy k ² ≫( m / M ) Δ E (rotational). In the case of neutral target molecules it is argued that the lower limit is given by \(k^{2}{\geqslant}1.65\varDelta{E}\) (rotational), and that the theory of Gerjuoy and Stein can be used at lower impacting energies.