Symmetries of highly excited atomic hydrogen:
Quadratic Zeeman splitting distorted by fine-structure effects

Using the classical mechanical perturbation approach and the semiclassical quantization rules we explain the spectrum of atomic hydrogen in a weak magnetic field in which fine structure of levels cannot be neglected. The general pattern of the spectrum turns out to be very different from the non-relativistic scheme. In particular, we point out the presence of another type of “exponentially narrow” doublet.