Question about organic spectroscopy (IR)

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SUMMARY

The discussion centers on the vibrational modes of molecules in infrared (IR) spectroscopy, specifically focusing on water (H2O). It is established that water exhibits bending and stretching modes, with the bending mode further categorized into scissoring, rocking, wagging, and twisting. The participant questions the assertion in their textbook that water only exhibits the scissoring mode, while also confirming that a non-linear molecule like water has three degrees of freedom calculated by the formula 3n-6, where n equals the number of atoms.

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  • Understanding of IR spectroscopy fundamentals
  • Knowledge of molecular vibrational modes
  • Familiarity with the degrees of freedom in molecular structures
  • Basic concepts of non-linear molecular geometry
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  • Research the different vibrational modes in IR spectroscopy
  • Study the specific vibrational modes of water (H2O) in detail
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Homework Statement



Hi. I'm starting to read about IR spectroscopy and I have a question. I know that there are 2 kinds of vibrational modes in molecules: bending and stretching, so in a molecule like water for example, how can I tell which one of the vibrational does it have?

What I mean is that I also know that there different types of modes within the bending category (scissoring, rocking, wagging and twisting), so which one of them is the right one (in the book that I'm reading it says that it can only have scissoring... why?)?

Thanks in advance!
 
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I don't think your book is right, but I could be wrong.

A non-linear molecule with three atoms should have 3 degrees of freedom, because 3n-6 = 3(3)-6 = 3, where n = number of atoms involved in the molecule.
 

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