A comparative study for the electron capture process O + ͑ 4 S 0 , 2 D 0 , 2 P 0 ͒ +He→ O͑ 3 P͒ +He + is reported. The cross sections are calculated using fully quantal and semiclassical molecular-orbital close-coupling ͑MOCC͒ approaches in the adiabatic representation. Detailed comparison of transition probabilities and cross sections is made from both MOCC approaches and displays close agreement above ϳ125 eV/ u. The remarkable discrepancies between the earlier semiclassical and quantal MOCC approaches may be attributed to the insufficient step-size resolution in their semiclassical calculation ͓M. Kimura et al., Phys. Rev. A 50, 4854 ͑1994͔͒. Our results have also been compared with experiment and found to be in good agreement.Considerable attention has been paid to investigations of charge transfer for collisions of O + and He in recent years ͓1-6͔ because of its importance in populating excited states of oxygen and producing its atomic emission spectra in various astronomical environments, such as comets ͓7͔, the terrestrial atmosphere ͓8͔, and supernova remnants ͓9͔. From the fundamental physics point of view, it is also very important to obtain detailed information on molecular structures and interactions for this system. The validity of classical, semiclassical, and quantal theories describing the collision systems may be checked by comparing measured and evaluated cross sections.Recently, two experimental studies on charge transfer between O + and He arrived at completely contradictive conclusions. The measurement of Kusakabe et al. ͓1͔ showed that the total capture cross sections from He by metastable O + ͑ 2 D 0 , 2 P 0 ͒ ions at keV energies are similar to or even greater than that for the ground-state O + ͑ 4 S 0 ͒, while Wolfrum et al. ͓4͔ found that the metastable cross sections are too small to be measurable and suggested that this unexpected behavior was caused by efficient suppression of electron capture by one of the metastable ions due to a competing collisionally induced inelastic transition into the companion metastable state. In view of such completely contradictory conclusions, Lindsay and Stebbings ͓5͔ remeasured chargetransfer cross sections for the same process. Their groundstate capture cross sections agree well with those of Wolfrum et al. ͓4͔ and Kusakabe et al. ͓1͔ above 2 keV and the metastable cross sections are also consistent with the mixed-state data of Kusakabe et al. ͓1͔. However, the large differences between the ground-state and metastable cross sections predicted by semiclassical calculations were not observed by Lindsay and Stebbings ͓5͔.More recently, Zhao et al. ͓6͔ reported a fully quantal investigation of charge transfer between O + and He using the molecular-orbital close-coupling ͑MOCC͒ method in the diabatic representation. They obtained good agreement with most of the measurements mentioned above. However, the calculations of Zhao et al. ͓6͔ reproduced neither the groundstate nor the metastable-state cross section, as predicted by the semiclassical MOCC approach o...
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