The Bethe theory for dissociative excitations and ionisation of H2+(1sσg) by electron impact

The revised Bethe theory for the inelastic scattering of charged particles by atoms and molecules is applied to H2+(1sσ g). In the 'reflection' approximation, the cross sections for the sum of all the discrete excitations σex, ionisation σ i and total excitations σtot given in an asymptotic expressions with three constants (the so-called Born asymptote) instead of two constants (the so-called Bethe asymptote) are accurately calculated. The Bethe asymptotes are given for comparison. It is shown that the ionisation cross sections given by the Born asymptote are most compatible with the experimental data, but the ones given by the Bethe asymptote are only valid at high incident energies. The calculated σex and σtot are also shown to be in excellent agreement with the experimental data at incident energies above 50 eV. The obtained cross sections (σtot + σi), σex and σtot are very sensitively dependent on the accuracy of the rotational-vibrational (RV) state distribution of H2+(1s σg) used to take the vibrational average. In general, the agreement between theory and experiment is consistent with that reported for one-element atomic targets. Thus it is concluded that the assumptions made to account for the nuclear vibrational and rotation motions, are valid for H2+ by electron impact. (author)