Question about organic spectroscopy (IR)

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In IR spectroscopy, molecules exhibit two primary vibrational modes: bending and stretching. For a non-linear molecule like water, which has three atoms, it possesses three degrees of freedom, leading to various vibrational modes. The bending modes include scissoring, rocking, wagging, and twisting, but in the case of water, only the scissoring mode is active in IR spectroscopy due to its molecular symmetry. This specificity arises from the molecule's geometry and the nature of its bonds. Understanding these vibrational modes is crucial for interpreting IR spectra accurately.
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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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