Diamagnetism of the Hydrogen Atom in the Quasi-Landau Regime

H-atom diamagnetism has been studied in the quasi-Landau regime with final magnetic states $|m_l^f=0\mathrm{}〉$, $|m_l^f=+1\mathrm{}〉$, $|m_l^f=0, +2\mathrm{}〉$, selectively excited by resonant two-photon absorption. All spectra exhibit detailed characteristic line structures. For $|m_l^f=+1\mathrm{}〉$ a new quasi-Landau resonance is discovered with a modulation spacing of $0.64\hslash {\omega }_c$ at $E=0\mathrm{}$, while the other final states are modulated with $1.5\hslash {\omega }_c$. The new resonance can be explained theoretically by a quasibound classical trajectory which lies outside the $z=0\mathrm{}$ symmetry plane.