Analysis of the features of energy spectra of excited states in their intersection region based on the exactly soluble quantum-mechanical problem

Modification of the structures of the spectra of excited states of a quantum system that is associated with the intersection (or approaching) of their energies and is revealed based on exactly soluble quantum-mechanical problem is illustrated based on the example of the model Landau representation of the mutually independent character of photon-roton excited states in degenerate liquid helium-II.