Trapping molecular ions formed via photo-associative ionization of ultracold atoms.

The formation of (40)Ca(2)(+) molecular ions is observed in a hybrid (40)Ca magneto-optical and ion trap system. The molecular ion formation process is determined to be photo-associative ionization of ultracold (40)Ca atoms. A lower bound for the two-body rate constant is found to be beta ≥ 2 ± 1 × 10(-15) cm(3) Hz. Ab initio molecular potential curves are calculated for the neutral Ca(2) and ionic Ca(2)(+) molecules and used in a model that identifies the photo-associative ionization pathway. As this technique does not require a separate photo-association laser, it could find use as a simple, robust method for producing ultracold molecular ions.