NEAR-THRESHOLD PHOTODETACHMENT OF THE LI- ION

The method of threshold-photodetachment spectroscopy has been used to measure the electron affinity of Li. Changes in the partial cross sections for the resolved h-nu + Li-(2(1)S) --> Li(2(2)S) + e-(epsilon-p) (2S-epsilon-p) and h-nu + Li-(2(1)S) --> Li(2(2)P) + e-(epsilon-s) (2P-epsilon-s) channels were separately investigated in the vicinity of the 2(2)P threshold. The near-threshold data in the 2P-epsilon-s channel were fitted to a Wigner law to determine a threshold photon energy of 19 884.8 +/- 1.6 cm-1. An electron affinity of 4980.9 +/- 1.6 cm-1 (617.6 +/- 0.2 meV) is obtained upon subtraction of the well-known 2(2)P excitation energy. The position of the Wigner cusp in the 2S-epsilon-p channel was measured to be 19 882.4 +/- 4.0 cm-1, in agreement with the more precise 2P-epsilon-s-channel threshold energy.