Electron impact excitation of metastable levels in O2+

Collision strengths have been calculated for electron-impact transitions between the O^{2 +} ground configuration terms ³P,¹D and ¹S, for energies up to 0.5 Ryd above excitation thresholds. The wavefunction expansion for the (e+O^{2 +}) system includes all O²⁺ terms for which the dominant configurations are 2s²2p² and 2s2p³. Configuration-interaction wavefunctions are used for the target states. These functions give accurate oscillator strengths for all transitions of the type 2s²2p²-2s2p³.

The collision strengths are calculated on solving systems of coupled integro-differential equations. The (³P-¹D) collision strength contains resonances of the type 2s²2p²(¹S)n/, and all collision strengths contain resonances of the type 2s2p³ nl.

The method used to obtain collision strengths for the (e + O²⁺) system is also used to calculate the positions of bound states for O⁺. It is found that inclusion of the 2s2p³ states of O²⁺ in the expansions gives a marked improvement in the agreement with experiment for the positions of the O⁺ bound states. The calculated positions of the near-threshold resonance states, 2s2p³(³D°)3s ²D° and 2s2p³(³P°)3s ²P°, are in satisfactory agreement with positions predicted from iso-electronic sequence extrapolations.

The collision strengths are integrated over Maxwell distributions for the velocity of the colliding electron, to obtain rate coefficients for use in astronomical applications. It is estimated that the errors in the computed coefficients should be less than 10%.

There are large differences between the present results and those obtained by Ormonde et al (1973). These differences are discussed and it is concluded that the results of Ormonde et al are in error.