The Mg(3s3d pi(3)D(J)). Kr((3) Pi(0+,0-)) and Mg(3s3d delta(3)D(J)). Kr((3) Delta(1)) valence excited states have been characterized via resonance enhanced two-photon ionization (R2PI) spectroscopy of transitions from the long-lived Mg(3s3p pi(3)P(J)). Kr((3) Pi(0+,0-)) metastable states of the MgKr van der Waals molecule. Because the excited Mg(3d) orbital is quite diffuse and the Kr atom can approach along the nodal axis of the aligned 3d orbital, minimizing repulsion, the MgKr(3s3d delta(3) Delta(1)) state is very strongly bound (D-0 = 1874 +/-80 cm(-1)), closely approaching the bond energy of the MgKr+ core ion (for which D-0 = 1891 +/- 80 cm(-1)). In contrast, the MgKr(3s3d pi(3) Pi(0-)) state is more weakly bound (D-0 = 587 +/- 80 cm(-1)), although it has a greater bond strength than the MgKr(3s3p pi(3) Pi(0-)) lower state (for which D-0 is 250 +/- 80 cm(-1)). We have also observed interesting spin-orbit effects which are attributed to mixing of Kr character into molecular orbitals which are nominally of Mg* excited-state character. (C) 1997 American Institute of Physics.