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The threshold behavior of the photodetachment cross section of negative ions as a function of photon frequency is usually described by the Wigner law. However, there is little theoretical guidance about the range or accuracy of the Wigner law. This paper reports the results of a model calculation using the zero-core-contribution (ZCC) approximation. Theoretical expressions for the leading correction to the Wigner law are developed, giving the range of validity of the Wigner law and the expected accuracy. The results, derived within the ZCC approximation, are relevant to extraction of electron affinities from experimental photodetachment data.

The corrosion of steel by lead-bismuth eutectic (LBE) is an important issue in proposed nuclear transmutation schemes. Steel samples were exposed to oxygen-controlled LBE at high temperature and exposure times that simulate actual reactor systems. Scanning electron microscopy (SEM), combined with energy-dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS), has been used to study post-exposure steel samples and unexposed controls. Our investigation of the reacted samples revealed preferential segregation of metals contained in the initial alloy formulations. Sputter depth profiling of the exposed annealed sample and cold-rolled sample showed a marked difference in oxide layer composition, depending on surface preparation. The annealed sample showed a complex oxide structure (iron oxide over chromium/iron oxide mixtures) of tens of microns thickness. The cold-rolled sample was covered with a rather simple, primarily chromium oxide layer of ~1 micron thickness. The cold-rolled sample had an order of magnitude less corrosion (i.e., both lower oxidation and less weight change) than the annealed sample.3

The A 2 A 1 -X 2 B 1 system of H 2 0 + has been observed, using laser absorption spectroscopy in a velocity-modulated discharge. A total of78 transitions between 14 794 and 15 475 em_, have been observed with an uncertainty ( 1 SD) of 0.02 em-1 , including 76 transitions in the (0,7,0)-(0,0,0) band and 2 in the (0,8,0):-(0,0,0) band. This species is important for cometary astronomy, and intriguing for molecular physics because of its prominent Renner-Teller interaction. Careful measurements were made of the relative intensities of the absorption lines, which were measured to an accuracy of 13% (1 SD). This is the first observation of the A-X transition in absorption; all previous data were obtained in emission with conventional grating spectroscopy. The transition frequencies of our new data are in good agreement with previous work, and have improved accuracy. The new data have definite rejection of the interfering lines from excited neutral H 2 that plagued previous work. Compared with previous work, the new data have the first quantitative measurement of intensities. The ratio of the Franck-Condon factors / 8 / / 7 = 0.99 ± 0.43 has been measured for the first time, where I,,= FCF[ (O,v',0)-(0,0,0) ].