Observation of new Rydberg series in the many-electron transition region of N ₂

Fluorescence excitation spectra produced through photoexcitation of N ₂ using synchrotron radiation in the spectral region between 50 and 62.5 nm have been obtained with a resolution of 0.004 nm. A broadband detector (in the 115-180 nm region) was employed to monitor fluorescence originated from neutral excited atomic nitrogen fragments which are produced through direct dissociation processes and predissociation from the well-known many-electron excited Rydberg states. We have identified a new Rydberg series (2 ²Π _g) 4sσ, a better resolved Rydberg (D ²Π _g) npσ series, and also the prominent Codling series converging to the D ²Π _g, and C ²Σ _u states of N ₂, respectively. By normalizing our relative fluorescence intensities to previously measured absolute fluorescence cross-section data we obtain the cross-section data of undispersed fluorescence in the 115-180 nm region. The fluorescence quantum yields for the present photodissociative excitation processes are found to be less than 0.05. The present results may provide important data for our understanding of competitions among the various decay channels of the many-electron transition states of N ₂.