Optical Spectroscopy of Slow, Highly Charged Ions after Collision with - Study of Electron Capture.

We have studied electron capture using a recoil ion source to produce beams of neon and argon ions, directed into a beam of atomic sodium. We have measured the wavelengths, relative intensities, and polarizations of the subsequent visible radiation due to DeltaN = -1 transitions. We have determined the partial capture cross sections of these systems as a function of velocity. In all systems studied, the partial cross sections at low velocity are largest for S levels, and at higher velocity are largest for the highest L levels; all cross sections are several orders of magnitude larger than Multichannel Landau-Zener model predictions. We have also determined the J distributions in the 9P and 9F manifolds of Ar^{ rm 7+*}, and have shown them to be statistical. Close coupling theory predicts that for slow collisions the electron is captured almost exclusively into the m _{rm L} = 0 state of the final system, yielding the highest possible polarization. As the velocity of the projectile increases, rotational coupling mixes in other m_{rm L} states, reducing the polarization. We have measured the polarization of the brightest lines in the spectra of the Ne^{rm 8+}, Ne^{rm 7+}, Ar ^{rm 9+} and Ar^ {rm 8+} + Na systems as a function of velocity. Lines corresponding to transitions from low L levels have no measurable polarization. For Ne ^{rm 8+} projectiles the polarization of light from high L levels shows no measurable change over the velocities used, for Ne^ {rm 7+} and Ar^{ rm 9+} it either remains constant or increases, and for Ar^{rm 8+ } it increases. We propose a theoretical explanation of this behavior. We have measured the wavelengths of strong transitions in the n = 9-8 manifold in the systems Ne^{rm 7+*} and Ar^{rm 7+*}. The wavelengths of the transitions 9S_{ rm 1/2} - 8P _{rm 1/2,3/2} in the Ne ^{rm 7+*} agree with the best QED predictions by Johnson to within experimental error.