Diamagnetic Rydberg atom: Confrontation of calculated and observed spectra

We present a detailed comparison of the observed and computed negative- and positive-energy spectrum of a Rydberg atom in a strong magnetic field. The study extends from -30 to +30 ${\mathrm{cm}}^{\mathrm{-}1}$ at a field of 6 T. The experimental resolution is sufficiently high to provide well-resolved spectra over the entire range. The spectrum calculated for hydrogen is in remarkable agreement with the spectrum observed in lithium.