Rydberg, effective, definition

Theoretical calculations of the dissociative recombination of Hj using the same approach as for the predissociation problem give cross sections that are smaller than all experimental results given in Table 1. However, these are only restricted, two-dimensional theoretical results, and cannot be used to draw definitive conclusions. Three-dimensional calculations, including all relevant electronic states, will be needed in the future. What seems clear at this point is that direct dissociative recombination, (X Ui) + e H3 (X E ) H + H + H or H + H2, is very slow. " For HeH" " it was found that the indirect mechanism, which involves vibrationally excited Rydberg states as intermediates, enhances the cross section.According to the preliminary calculations, the effect of the indirect mechanism is even more pronounced for Hj. Model calculations have shown that channel mixing effects can enhance the DR cross section substantially when the indirect mechanism is taken into... 

Precision spectroscopy of helium has not, in general, been of importance for fundamental constants with the single conspicuous exception of optical spectroscopy of ionized helium. Taking advantage of the zero spin nucleus, E. Kessler was able to accomplish the last definitive Rydberg measurement before the advent of Doppler-free spectroscopy [20]. Beyond this, when two electrons are present, the physical constants and the QED effects are joined by the problem of how the two electrons learn to live with one another. This subject is rich and diverse and is treated to some extent in the contribution of Professor Fano to this Conference. 

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