Electron affinity of Li: A state-selective measurement

We have investigated the threshold of photodetachment of Li- leading to the formation of the residual Li atom in the 2p(2)P state. The excited residual atom was selectively photoionized via an intermediate Rydberg state and the resulting Li+ ion was detected. A collinear laser-ion beam geometry enabled both high resolution and sensitivity to be attained. We have demonstrated the potential of this state-selective photodetachment spectroscopic method by improving the accuracy of Li electron affinity measurements an order of magnitude. From a fit to the Wigner law in the threshold region, we obtained a Li electron affinity of 0.618 049(20) eV.