ELECTRON-AFFINITY OF LI - A STATE-SELECTIVE MEASUREMENT

We have investigated the threshold of photodetachment of Li- leading t o the formation of the residual Li atom in the 2p(2)P state. The excit ed residual atom was selectively photoionized via an intermediate Rydb erg state and the resulting Li+ ion was detected. A collinear laser-io n beam geometry enabled both high resolution and sensitivity to be att ained. We have demonstrated the potential of this state-selective phot odetachment spectroscopic method by improving the accuracy of Li elect ron affinity measurements an order of magnitude. From a fit to the Wig ner law in the threshold region, we obtained a Li electron affinity of 0.618 049(20) eV.