Interpreting IR/Raman Spectra Using Character Tables

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To interpret IR/Raman data, understanding the symmetry of the molecular system is crucial. The designations "u" (ungerade) and "g" (gerade) relate to the symmetry of the wave functions, indicating whether the modes are symmetric or antisymmetric. To assign these modes to specific molecular motions such as stretching or bending, one should refer to the character table corresponding to the molecule's point group. Character tables provide detailed information on which vibrational modes are active in IR or Raman spectroscopy. These tables can often be found online or in specific chemistry textbooks, making them accessible for further analysis.
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hi,

I am trying to interpret some data which have been calculated for IR/Raman but I don't know how to interpret them exactly. The schema says
mode \nu
1 b_u 82
1 a_g 216
2 b_g 239

I presume that the u/g are gerade/ungerade from the bonding/antibonding wave functions but how to assign these informations into stretch, bend etc. Is there a table where one can look these values up?

How to proceed any help appreciated. Thanks in advance.

 
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greisen said:
hi,

I am trying to interpret some data which have been calculated for IR/Raman but I don't know how to interpret them exactly. The schema says
mode \nu
1 b_u 82
1 a_g 216
2 b_g 239

I presume that the u/g are gerade/ungerade from the bonding/antibonding wave functions but how to assign these informations into stretch, bend etc. Is there a table where one can look these values up?

How to proceed any help appreciated. Thanks in advance.
You have to find out the symmetry of the system and then look at the character table for that point group. The meanings of a and b etc are all in the character table and will tell you which motions (bend, stretch) are raman active and which are not.
 
hi,

A character table - is it possible to find that online or does one have to consult a certain book?
 

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