Triangular model

The sign of the metal is negative in agreement with experiment. A study of the triangular model gives the charges as a function of the bond integral. It shows that... 

Thus for the linear model k2b will be smaller than k2a roughly by a factor exp (—O.SOv /T) where is expressed in cm-1. On the other hand for an isosceles triangular model, with Cl at the apex, k2a, and k2b are equal. Therefore the differences in v, calculated from R for the two models will depend on the variation of the contribution of k2bjk2a to R. 

The frequency ratios needed for the calculation are rather insensitive to force constants. For the linear model, ratios are calculated with the Wheeler, Topley, Eyring potential. For the triangular model the frequency ratios have been taken from the frequency values for HTO and H20, since the product rule value for the water molecule comes within the range of a number of triangular complexes and since the and vL ratios are practically the same as for HTC1, HaCl. Inasmuch as the bending frequency makes only a minor correction, this is not too important an approximation. The frequency ratios for the HaCl transition states are listed in Table IV. One also needs to estimate now a+ and... 

The first studies of the Mossbauer spectra of carbonyl clusters were made on Fe3(CO)i2 and as two of the Fe atoms were markedly different from the third, a symmetric linear model was proposed 148, 164, 227). A later study which demonstrated the Mossbauer equivalence of Fe3(CO)i2 and Fe3(CO)nH , the structure of which was known 303), led to the postulation of the correct unsymmetrical triangular model 134). 

A triangular model, described by Westerberg, is not only less accurate but also less reproducible than dropping a perpendicular >. Several rules outlined by Kaiser and Klier ) for drawing a separating line between unresolved peaks give large errors with realistic peaks >. 

Pig. 5-10. Form of the completely reduced representation for the plane equilateral triangular model of the carbonate ion, CO3 , an example of the group Bsj. The symbols indicate the irreducible representation corresponding to each nonmixing block. 

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