The metal ion-complex Mg-24(+)-Ar has been prepared in a pulsed nozzle/laser vaporization source, mass selected with a reflection time-of-flight mass spectrometer and studied with photodissociation spectroscopy at high resolution. The (5,0) band of the A (2) Pi(r)<--X (2) Sigma(+) transition has been rotationally analyzed and the rotational constants, B " = 0.1409(7) cm(-1) and B’ = 0.1836(8) cm(-1), and spin-orbit constant, A’ = 73.94(2) cm(-1), have been determined. The bond distances in the ground and excited states of the complex (r "(0) = 2.88 Angstrom, r’(5) = 2.52 Angstrom)) compare well with the values predicted by theory, and they confirm the suspected nature of the electrostatic bonding in this system.