Ab initioCI calculation of O2+predissociation phenomena induced by a spin-orbit coupling mechanism

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Abstract
Potential curves have been calculated for ground and excited states of the O2 + ion employing MRD-CI treatment in a series of AO basis sets including one of a double-zeta plus polarization quality. Over-all good agreement is obtained for structural parameters of the various states as well as for vertical and adiabatic transition energies; the D e value for the 2Π g ground state is obtained as 6·20 eV in the best treatment (using bond functions), compared to the experimental value of 6·78 eV. The crossing of the various potential curves are described very well in the theoretical treatment with the b 4Σ g - species being intersected by the 4Σ g + and f 4Π g curves at υ = 4–5 and υ = 6–7, as compared to experimental inferences based on observed predissociation onsets of υ = 4 (N = 9) and υ = 7 respectively. Spin-orbit coupling matrix elements for both one- and two-electron interactions have been computed using the large-scale CI wavefunctions. The calculated X 2Π g spin-orbit coupling constants agree with their experimental values to within better than 5 per cent and show the correct behaviour with vibrational quantum number. Almost quantitative agreement is found between theory and experiment for the radiationless transition probabilities between b 4Σ g - - 4Σ g + and b 4Σ g - - f 4Π g as a function of υ, whereby the required continuum vibrational species have been obtained in a discrete representation; dipole transition strengths are also described quite accurately in the calculations. Finally a mechanism is proposed for the predissociation of the B 2Σ g - state for the separate process with onsets at υ = 0 and υ = 3.

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