Harmonic vibration wavenumber

Since vibrational spectra of S2O2 have not yet been observed, the force constants calculated by ab initio MO methods were used to predict the harmonic vibrational wavenumbers of ds-S202 (C2v) and trans-S202 (C2I1) see Table 3 [34, 57]. 

For a precise determination of the structures, ab initio calculations on the energies of formation and characteristic harmonic wavenumbers have been performed at the HF and MP2/6-31G(d,p) level of theory with the Gaussian 92 program for the species of interest . The ab initio calculated energies and harmonic vibrational wavenumbers are given in Table 5. 

TABLE 5. Ab initio calculated energies (Joule)" and harmonic vibrational wavenumbers (cm ) of the species of interest ... 

Often the original structure determination will have involved some uncorrected vibrational averaging effects it may be an r0 or an r, structure.28 However, once /2, or some approximation to /3, has been determined it is possible to correct r to re and obtain an improved equilibrium structure (in most cases this correction can be made directly from the cubic anharmonic calculation, but in some cases the calculation will allow unobserved a. values to be determined, perhaps for other isotopic species, etc.). Similarly, it is often true that the harmonic field /2 is calculated from the observed fundamentals (the v values) rather than the harmonic vibration wavenumbers (the to values), for want of information on the corrections. However, once /4, or some approximation to/4, has been determined, it may be used to calculate a complete set of x values and hence to calculate all the corrections to obtain the co values. Thus the calculation of re and may be improved from a knowledge of /3 and /4. 

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