ABSTRACT
The molecular vibrations can be described in the framework of the quantum theory of the harmonic oscillator. This approximation, however, ignores the coupling of different normal mode vibrations as well as the non-parabolic profile of the potential energy in which the collective oscillation of the atoms happens. The complex structure of the infrared (IR) absorption spectra requires methods able to correctly interpret the relationship between the normal mode vibrations and the experimental frequency values given by different spectral peaks. Both IR and Raman spectroscopy methods provide a unique spectral fingerprint of a certain molecule. The harmonic oscillator is a highly idealized model, where the oscillator’s fundamental frequency of vibration is independent of the amplitude of the vibrations. In order to unequivocally identify the molecular fingerprint given by the vibrational absorption spectrum one needs to correctly assign the normal mode frequency vibrations to different absorption peaks from the spectrum.
