1 / 4

Lecture 13 APPLICATIONS OF GROUP THEORY 1) IR and Raman spectroscopy. Normal modes of H 2 O

Lecture 13 APPLICATIONS OF GROUP THEORY 1) IR and Raman spectroscopy. Normal modes of H 2 O. Three normal vibrations of H 2 O transform as 2 A 1 and 1 B 2 representations. 2) Selection rules for IR and Raman active bands.

chelsea-hamilton
Télécharger la présentation

Lecture 13 APPLICATIONS OF GROUP THEORY 1) IR and Raman spectroscopy. Normal modes of H 2 O

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 13 APPLICATIONS OF GROUP THEORY1) IR and Raman spectroscopy. Normal modes of H2O Three normal vibrations of H2O transform as 2 A1 and 1 B2 representations

  2. 2) Selection rules for IR and Raman active bands • A normal vibration is IR active if it transforms as x, y, z or any of their linear combinations. • A normal vibration is Raman active if it transforms as quadratic functions x2, y2, z2, xy, xz or yz.

  3. 3) Selected vibrational modes • For polyatomic species considering full set of normal modes is usually very time consuming. • Consideration of only selected vibrational modes is simpler and often very important. The modes may be, for example, only stretching modes of a particular type. • Combined with group theoretical analysis, vibration spectroscopy may allow for distinction of isomers. • In the simplest cases the isomers can be distinguished by the number of stretching bands observed for particular bonds in IR spectra of these isomers (see the example below). • Let us see, how group theory can help assign the proper configuration to these complexes. (a) assign the isomers to the appropriate symmetry point groups (b) chose vectors, 1 and 2, of two Pd-N bonds a basis function for a reducible representation corresponding to Pd-N stretching modes. (c) build the appropriate reducible representations, decompose them and find out which modes are IR active.

  4. 4) IR and Raman spectroscopy based structure elucidation • Consider two possible structures of Co(CO)5+ (HF solution with [(CF3)3BF-] counterion), D3h and C4v. • In an experiment two IR CO-stretching bands (n, 2140, 2121 cm-1) and three Raman CO-stretching bands (n, 2195, 2152, 2121 cm-1) are observed. Thus, Co(CO)5+ is trigonal bipyramidal (D3h). • Consider three possible structures of XeF5-, D3h, C4v and D5h. • In an experiment XeF5- exhibited in total three bands in the IR: 550, 290, 274 cm-1 and three bands in its Raman spectrum: 502, 423, 377 cm-1. This result matches D5h symmetry only. • Thus XeF5- is pentagonal planar (D5h). Total number of bands / number of stretching bands:

More Related