SPECTROSCOPIC CHARACTERIZATION OF THE EXCITED VALENCE MGXE(3D-DELTA(3)DELTA(1)), MGXE(3D-PI(3)PI(0)), AND MGXE(3D-SIGMA(3)SIGMA(-DER-WAALS STATES()) VAN)

The Mg(3s3d sigma(3)D(J)). Xe((3) Sigma(+)), Mg(3s3d pi(3)D(J)). Xe((3 ) Pi(0+,0-)), and Mg(3s3d delta(3)D(J)). Xe((3) Delta(1)) excited stat es have been characterized via resonance enhanced two-photon ionizatio n (R2PI) spectroscopy of transitions from the long-lived Mg(3s3p pi(3) P(J)). Xe((3) Pi(0+,0-)), metastable states of the MgXe van der Waals molecule. Because the excited Mg(3d) orbital is quite diffuse and the Xe atom can approach along the nodal axis of the aligned 3d orbital, m inimizing repulsion, the MgXe(3s3d delta(3) Delta(1)) state (D-0= 3160 +/- 150 cm(-1)) is even more strongly bound than the MgXe+ core ion ( for which D-0 = 2848 +/- 150 cm(-1)). The MgXe(3d sigma(3) Sigma(+)) s tate (D-0 = 1262 +/- 150 cm(-1)) and the MgXe(3d pi(3) Pi(0-)) state ( D-0 = 1229 +/- 150 cm(-1)) are much less bound. However, the potential curves of these two states are quite different, and it is suggested t hat the MgXe(''3d sigma''(3) Sigma(+)) State is bound only because of substantial mixing of Mg(4p sigma) Rydberg character into the wave fun ction. Interesting spin-orbit and spin-spin effects, detected and anal yzed from the rotational structure of the vibrational bands, are attri buted to mixing of some Xe character into molecular orbitals nominally of Mg excited state character. (C) 1997 American Institute of Physic s.