BA 6SNL-]7SNL AND 10SNL DOUBLE-RYDBERG SPECTRA AND STRAY ELECTRIC-FIELD EFFECTS

We present an analysis of the effect of the stray electric field on 7snl and 10snl double-Rydberg spectra for n = 12-15. To excite these states we use the Stark switching technique to populate high l, along with the isolated core excitation (ICE) method. The 7snl spectra show a single peak for each l excited, while as observed for 8dnl states, the 10snl spectra show a multiple peak structure common to all l (for n > 12). This structure is explained by taking into account a 1 V cm-1 stray electric field which l mixes the 6snl levels from which the 10snl are excited. Application of a small, less-than-or-equal-to 10 V cm-1, static electric field allows us to identify the difference l components in the 10snl spectra. With the spectral components identified in this manner, we have measured the 7snl and 10snl quantum defects and have determined their l dependence. Our results show that the Coulomb electron-electron interaction is essentially dipolar, with an l-5 dependence. The quadrupolar, l-9 dependence, has a maximum contribution of only 15%. We have observed the resolved K structure of the 10s n = 12 l = 11 double-Rydberg state.