OPTICAL-TRANSITION IN THE NEGATIVE MAGNESIUM-ION

A search for the Mg- ion detected via the 2p3p34S2p63s3p24P transition is described. The Mg+Mg-4S two-step charge-exchange process is investigated and compared with the recently observed Be+Be-S process. Analysis of the optical spectra shows that the cross section for producing the -S state by beam-foil or beam-gas collisions is much larger, a factor of 30 or more, than for producing -4S. The search has been concentrated in the 28602950- region that covers the two wavelengths 2921 and 2895 recently proposed theoretically for the above transition. None of the spectral lines observed within the spectral region studied exhibits the properties of a negative ion. While the possibility of observing the Mg-4S-P transition at 29214 [D. R. Beck, Phys. Rev. A 40, 2887 (1989)] can be excluded, the 2895 3 region [C. Froese Fischer, Phys. Rev. A 41 3481 (1990)] is more complicated since it contains a so far unidentified spectral line. We can assign this line to the quintet spectrum of Mg i. This assignment is supported by four lines forming a closed loop, consistent with optical transitions between the 2p53s3ps and 2p53s3p configurations, and by multiconfiguration Hartree-Fock calculations. The lack of experimental observations of the predicted Mg- ion is discussed. © 1990 The American Physical Society.