Lecture 6

Lecture 6

1. Once the stretching modes have been found you have in phase and out of ohase combinations of individual bond stretches

2. SALCs

   • Symmetry Adapted Linear Combinations
   • projecton operators are used to find SALCs

3. ·

   • choose an OH vector and see how it transforms using the tables (C2v for H2O)
     • multiply the result by the table values (X) in the chosen irrep
       • do the same for any remaining irreps found after reducing
         • this shows whether a bond is pointing in or out simultaneously to the other bonds

4. SALCs should be normalized

   • the sum of the squares of the coefficients needs to equal 1

5. If you try to calculate a non-existent SALC then you get 0

6. It is very important to say which way your axis lie before you do SALC calculations as this determines which bonds point in or out

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