Wavelengths of over 3000 americium lines have been measured with a 30-ft spectrograph, and intensities compared in a number of sources leading to assignment of most lines as Am i or Am ii. Hyperfine structure and isotope shifts have been measured in high orders for many lines. In this paper only the classified lines are listed, consisting of 173 Am ii lines representing transitions between 5 odd levels and 63 even levels, and 112 Am i transitions between 12 odd levels and 39 even levels. Although the number of classified lines is less than 10% of the total almost all the strong lines are included. The ground states of Am ii and Am i are 5f77s and 5f77s2, respectively. The ionization potential of Am i is 6.0 ev. Most of the levels have not been identified but are believed to be built on 5f66d instead of 5f7. The binding energy of 5f7 compared with 5f66d is 10 000 cm−1 smaller than in Eu and is related to the higher valences found in the 5f elements compared with the 4f elements.
The ratio of the nuclear magnetic moments of Am241 and Am243 is μ241/μ243=1.008.
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