Laser-induced fluorescence (LIF) measurements of the Mg(3s3p P-1(1)).Xe((II1)-I-1)<--Mg(3s3s(1)S(0)).Xe(X(1) Sigma(+)) transition of the jet-cooled MgXe complex have revealed that the ground X(1) Sigma(+) state is quite weakly bound (D-e(n) approximate to 100 cm(-1)) compared to the (II1)-I-1 excited state (D'(e) approximate to 1500 cm(-1)), and that the bond length in the (II1)-I-1 excited state is some 1.5 Angstrom shorter. Here we report the observation of dispersed fluorescence spectra from single vibrational levels of the (II1)-I-1 state, consisting mainly of oscillatory bound-free continua which extend over some 7500 cm(-1). These spectra are analyzed using the semiclassical method of Child and LeRoy to determine the repulsive portion of the Mg.Xe(X(1) Sigma(+)) interaction potential up to nearly 1 eV in energy. Attempts were made to fit the experimental potential curves to several simple analytical functions, with a two-term Buckingham-type function yielding the best representation. A comparison of the repulsive portion of the Mg.Xe(X(1) Sigma) potential curve with that of the analogous Na.Xe(X(2) Sigma) curve determined similarly by Zimmerman and co-workers shows that the Na.Xe curve is even less repulsive than the Mg.Xe curve, even though the Mg.Xe potential is itself quite ''soft''. This can be rationalized by the ability of the more diffuse Na(3s) electron to ''back-polarize'' (spo hybridize) away from the Xe atom compared to the two Mg(3s(2)) electrons, thus reducing repulsion.