Conclusion

Abstract

In this book we have discussed the effects of nonlinearity in the vibrational-rotational motion in polyatomic molecules and in simple molecular crystals like N₂,CO, etc. This nonlinearity is revealed most transparently at high excitation levels of the vibrational/rotational mode in the presence of a point symmetry of the initial Hamiltonian. Then the strong excitation leads to the dynamical violation of the initial symmetry. The IR spectra under insufficient resolution demonstrate lowered symmetry in the rotational spectra. For example, in place of the octahedral symmetry in the molecule XY₄ the symmetry C_3v of a symmetric top will be observed. Thus the determination of the real symmetry of the intramolecular Hamiltonian, and the reconstruction of the potential energy surface of the intramolecular interaction requires the great enhancement in the resolution of the IR spectral lines (~ 10⁶÷10⁻⁸ cm⁻¹). This will enable the determination of the interaction with nuclear spins and the correct interpretation of the lines in IR spectra as well.