[en] A new approach to calculate energy levels and wave functions of polyatomic molecules with a definite geometric structure of the system assumed from the very beginning has been suggested. The effect of nuclear vibrations has been taken into account explicitly when separating variables in the Hamiltonian of the electronic state problem. The problem of the energy matrix formation has been discussed. It has been shown that some common patterns in higher-order vibrational spectra and in vibronic spectra can be explained without using concepts of anharmonism and changing the potential well parameters for an electron-excited state as compared to those for the ground state. (authors)