| Summary: | Rotationally resolved zero-kinetic-energy (ZEKE) photoelectron spectra of the X^2 Σ_(g)^(+) (V^(+) = 0,1)← X^(1)Σ_(g)^(+) (v=0) bands of nitrogen have been recorded. The spectra show unexpected rotational-line intensities. The intensity distortions are explained by channel interactions. The strong S and U branches [N^(+) 0 J^(primeprime)) = +2 and +4, respectively] of the (1-0) band borrow intensity from a nearly degenerate Rydberg state, converging to an electronic excited state of the ion, by a complex resonance mechanism. Field-induced rotational autoionization is shown to enhance the O branch and M branch [N^(+) 0 J^(primeprime)) = -2 and -4] intensity of the (O-O) band. Recording ZEKE spectra with extraction fields of 10-100V/cm appears to be an attractive and powerful way of obtaining spectroscopic information on Rydberg states with simultaneously high principal quantum number n and high total-angular-momentum quantum number J.
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