Numerical study of the quasi-Landau resonances of sodium

By diagonalizing the diamagnetic Hamiltonian, with a basis set composed of potential-model eigenstates of field-free alkali-metal atoms, we have calculated the quasi-Landau resonances (QLR) of sodium (even parity, magnetic quantum number m=-2,-1) and obtained results which agree remarkably well with the experiment of Castro et al. [Phys. Rev. Lett. 45, 1780 (1980)]. The agreement suggests that, up to a close vicinity of the ionization threshold, the continuum states contribute little to the shaping of quasi-Landau modulations. Fourier transforms of our numerical QLR reveal two energy spacings which correspond, respectively, to 1.5ħ${\mathrm{\omega }}_{\mathit{c}}$ and 0.64ħ${\mathrm{\omega }}_{\mathit{c}}$ at the ionization threshold.