The weakly bound Ca(4s4dÏƒ 3D3) Â· Ar[3âˆ‘+] state has been characterized by means of R2PI (Resonant Two-Photon Ionization) spectroscopy, using transitions from the Ca(4s4p Ï€3P0) Â· Ar[3II0-] metastable state prepared in a laser-vaporization/supersonic jet source. Because several of the vibrational levels are above the dissociation limit [to Ca(4s4d3D3) + Ar(1S0)], it is concluded that there must be a substantial maximum in the Ca((4s4dÏƒ 3D3) Â· Ar[3âˆ‘+] potential curve (>200 cm-1) at large R (>4.0 Ã…). This is discussed, and shown to be consistent with our earlier ideas of "penetration" of outerlobes of electron density of metal atom excited states by RG (rare-gas) atoms. Perturbations observed, due to possible potential curve crossings with states of different electronic symmetry, are also discussed. Â© 1999 American Institute of Physics.