Experimental Evidence that the 6s6p 3PJ States of Cs- Are Shape Resonances

An experimental study of the previously unobserved and controversial Cs-(6s6p PJo3) states has been conducted using a combination of infrared laser and storage ring experiments. This first application of photodetachment spectroscopy to the study of low-lying resonances in atomic negative ions has resulted in the observation of a narrow resonance structure, lying only 8.0(3) meV above the first detachment threshold of Cs-. The storage ring experiments suggest that all fine structure levels of the 6s6p configuration are unbound, thereby eliminating possibly the only serious candidate for a stable atomic negative ion with opposite parity bound states.