The method of threshold-photodetachment spectroscopy has been used to measure the electron aSnity of Li. Changes in the partial cross sections for the resolved hv+Li (2'S)~Li(2 S)+e (ep) ( Sap) and h v+Li (2 'S)~Li(2 P)+e (es) ( Pcs) channels were separately investigated in the vicinity of the 2 P threshold. The near-threshold data in the Pcs channel were fitted to a Wigner law to determine a threshold photon energy of 19884.8+1.6 cm '. An electron affinity of 4980.9+1.6 cm (617.6+0.2 meV) is obtained upon subtraction of the well-known 2 P excitation energy. The position of the Wigner cusp in the Sap channel was measured to be 19882.4+4.0 cm ', in agreement with the more precise Pcs-channel threshold energy. PACS number(s): 32.80.Fb, 35.10.Hn 610 596248 608 615

No abstract

No abstract

No abstract

The metastable Be anion has been experimentally investigated using a crossed lasernegative-ionbeam apparatus. The Be(2'P) electron affinity of 261+10 meV has been determined by photodetachedelectron spectroscopy. It is also demonstrated that the Be(2'P) excitation energy of 2.723+0.007 eV can be determined by means of a hybrid technique involving the use of both autodetachedand photodetached-electron spectroscopies.PACS number (s): 32.80.Fb, 35.10.Hn We present the results of an experimental investigation of the metastable Be anion using a crossed lasernegative-ion-beam apparatus. The electron affinity and excitation energy of the Be(2 P) state have been measured by the use of the techniques of photodetachedelectron spectroscopy (PES) and autodetachedand photodetached-electron spectroscopy (APES), respectively. The Be ion was first observed over two decades ago by Bethge, Heinicke, and Baumann [1] in mass spectra of ions extracted from a negative-ion source. Subsequently, a theoretical investigation of the structure of this ion was made by Weiss [2]. It was demonstrated that although the ion is not stable, an extra electron can be attached to the Be atom in the metastable (2s2p ) P state to form a long-lived Be ion in the spin-aligned (2s2p ) P state.Weiss predicted that the electron affinity of the parent Be(2 P) atom would be about 240 meV. The 2 P state in Be is relatively long lived as a result of being metastable against Coulomb autodetachment. Eventually the ion autodetaches via the weaker magnetic interactions. A partial energy-level diagram of the Be and Be systems and the relevant transitions is shown in Fig. 1. There exists a differential metastability among the three fine-structure levels of the 2 P state since each couples with a different strength to the continuum. Calculations of these level lifetimes [3 -5] and the fine-structure intervals [6] were subsequently made. The first experimental investigation of the lifetimes of levels associated with the 2 "P state was made by Bae and Peterson [7] via autodetachment measurements. Accurate lifetimes of these levels have been recently reported by Balling et al. [8]. The J= -, ' level was found to be 180 times longer lived than the J= -, ', -, ' levels. Since the early work of Weiss, there have been several other theoretical estimates [6,9,10] of the electron affinity of Be(2 P) Currently the . most accurate calculation, that of Bunge [10],yields a value of 276. 1+6.5 meV.