A SHAPE RESONANCE OBSERVED IN FAST COLLISIONS OF LI- IONS WITH GAS TARGETS

A shape resonance state in the Li- ion, identified as the 2s2p P-3(o) state, has been populated in 100 keV collisions with a He gas target. The resonance was observed via zero-degree electron detachment spectro scopy in which kinematic shifting and doubling were exploited in the d etection of the very low energy electrons. The electrons ejected via t he resonance gave rise to structures in the electron energy spectra th at were disposed about a continuum cusp. These structures corresponded to forward- and backward-directed emission in the projectile frame. L aser photodetached electron spectroscopy was used to accurately calibr ate the electron energy scale and to determine the spectrometer resolu tion function. Preliminary analysis indicates that the measured positi on and width of the resonant state agree with theoretical values.