The lowest energy interval of Es II was discovered by Worden et al. (70.5) by using their accurate wavenumber measurements and sensitive spark line observations (67.2). New spectrograms were obtained from better samples of einsteinium, the number of lines of both Es I and Es II being increased from 53 to 290 (74.5). This second step led to 9 new upper levels and to some configuration assignments, in particular the lowest level pair of 5f¹¹7p.

The early measurement of the hfs constants was improved for the A-factors and revised for the g-factors of the lowest levels.

Using the line list of (74.5) and accurate level predictions resulting from parametric studies with generalized least squares of all 5f^N7s configurations (80.4), the search for low odd levels was resumed and both levels built on the lowest J = 11/2 level of the core 5f¹¹ were determined. Two other systems of levels were left unconnected with the ground level: they involved pairs of lines with wavenumber difference of 535.15 cm^-1 and 494.92 cm^-1 and hfs width differences larger than 10 cm ^-1 which precluded the Es I assignement. Systematic measurement of spectra photographed at Argonne in the late 70's by Conway and Worden have led Crosswhite and Crosswhite (unp.17) to unify these levels in an unique system and to discover several upper levels. The Slater-Condon method applied to the configuration 5f¹¹7s leads to unambiguous labels for the 8 odd levels (unp.9).

Tentative assignments are given to some even levels. Twenty-five out of the 87 strongest lines reported in (74.5) are interpreted as Es II transitions and the analysis is still in progress.