Anharmonicity constants from overtone progressions

From the overtone progressions of molecules in solution it may be possible to obtain the effect of intermolecular interaction on the ground state properties of the molecule under investigation, since a frequency change with the used solvent can be observed (Kiefer and Bernstein, 1973b). 

2 Accurate determination of excited state repulsive potential functions of diatomic molecules in the gaseous phase 

As discussed above, continuum resonance occurs when the excitation laser energy is higher than the dissociation limit of an excited, bound electronic state or directly with purely repulsive states. Continuum resonance Raman spectra of gaseous molecules are very sensitive to the position and shape of the potential functions involved in this type of light scattering as well as to the electronic transition moments between ground and excited states. Since it is possible to calculate the relevant spectra using both the KHD 

Section 6.1.2.2 in contributed by W. Kiefer, Wurzburg and M. Spiekermann, Ltibeck 

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The resonance Raman spectrum of K4[Mo2C18] has been reinvestigated using 488.0 and 514.5 nm excitation. An enormous enhancement of the intensity of the Mo—Mo stretching mode relative to the intensity of other fundamentals was observed and an overtone progression in Vj to 5vj identified. From these data the harmonic frequency and anharmonicity constant X, were calculated as 347.1 + 0.5 cm -1... 

The principal progression-forming mode, Vi, is almost harmonic up to vibrational quantum number 6, with the anharmonicity constant Xi, 0.2cm . The overtone band wavenumbers derived from the calculation differ from the experimental values by a few wavenumbers as the vibrational quantum number increases. Other modes show only one or two harmonics. 

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