Pseudorotational excitation spectrum of the cyclobutane molecule: I. The C4H8 isotope

A rigorous model for the description of the spectrum of excitations of nonrigid motion of the pseudorotational type of the cyclobutane molecule in a nondegenerate electronic state is constructed. The construction is based on the symmetry-group chain methods. The model constructed explains a number of qualitative features of this spectrum that follow from the analysis of spectral data. As a first approximation, the isotopically symmetric combination C4H8 is considered