CHARACTERIZATION OF THE FIRST EXCITED (1)PI(1) AND GROUND CHI(1)SIGMA(-]CHI(1)SIGMA(+) BOUND-FREE EMISSION-SPECTRA() STATES OF MGXE .2. ANALYSIS OF (1)PI(1))

Laser-induced fluorescence (LIF) measurements of the Mg(3s3p P-1(1)).X e((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 th at the bond length in the (II1)-I-1 excited state is some 1.5 Angstrom shorter. Here we report the observation of dispersed fluorescence spe ctra 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) S igma(+)) interaction potential up to nearly 1 eV in energy. Attempts w ere made to fit the experimental potential curves to several simple an alytical 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 rati onalized by the ability of the more diffuse Na(3s) electron to ''back- polarize'' (spo hybridize) away from the Xe atom compared to the two M g(3s(2)) electrons, thus reducing repulsion.