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

The Mg(3s3d pi(3)D(J)). Kr((3) Pi(0+,0-)) and Mg(3s3d delta(3)D(J)). K r((3) Delta(1)) valence excited states have been characterized via res onance enhanced two-photon ionization (R2PI) spectroscopy of transitio ns from the long-lived Mg(3s3p pi(3)P(J)). Kr((3) Pi(0+,0-)) metastabl e 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 noda l 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 w hich 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 h as a greater bond strength than the MgKr(3s3p pi(3) Pi(0-)) lower stat e (for which D-0 is 250 +/- 80 cm(-1)). We have also observed interest ing spin-orbit effects which are attributed to mixing of Kr character into molecular orbitals which are nominally of Mg excited-state chara cter. (C) 1997 American Institute of Physics.