Rotationally resolved zero-kinetic-energy photoelectron spectrum of nitrogen

Rotationally resolved zero-kinetic-energy (ZEKE) photoelectron spectra of the X ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$(${\mathrm{v}}^{+}$=0,1) ←X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$(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 [(${\mathit{N}}^{+}$-J’ ’)=+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 [(${\mathit{N}}^{+}$-J’ ’)=-2 and -4] intensity of the (0-0) band. Recording ZEKE spectra with extraction fields of 10–100 V/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.