The assignment of molecular symmetry from vibrational spectra
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
190-191
2025-08-30
354
The assignment of molecular symmetry from vibrational spectra
An important application of vibrational spectra is the identification of molecular symmetry and hence shape and structure. An especially important example arises in metal carbonyls in which CO molecules are bound to a metal atom. Vibrational spectra are especially useful because the CO stretch is responsible for very strong characteristic absorptions between 1850 and 2200 cm–1 (Section 22.5). The set of characters obtained by considering the symmetries of the displacements of atoms are often found not to correspond to any of the rows in the character table. How ever, because the character table is a complete summary of the symmetry properties of an object, the characters that have been determined must correspond to a sum of two or more of the rows in the table. In such cases we say that the displacements span a reducible representation. Our task is to find the irreducible representations that they span. To do so, we identify the rows in the character table that must be added together to reproduce the set of characters that we have obtained. This process is called reducing a representation. In some cases the reduction is obvious; in others it may be carried out systematically by using a procedure explained in Section 6.9.
Figure 6.18 The modes of Ni (CO)4 that correspond to the stretching of CO bonds.
Table 6.6 The Td character table
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