This section supplements the discussion in Section 19.2 starting on page 712 covering polyatomic vibrations. In particular, the animations below bring Figure 19.6 on page 715 to life.
The top panel shows the CO2 molecule, while the bottom shows H2O. In each panel, you can set the variables Symmetric, Bend, and Antisymmetric to either 1 (to enable that mode) or to 0 (to disable that mode). Make your selection, then click on the top graph to see the mode or modes you have selected animated. The equilibrium position of each atom will appear as stationary green spots beneath the vibrating molecules.
The numerical values (in cm–1 units) of the three normal mode frequencies, w1, w2, and w3, are shown (as listed on page 713), and the lower graph in each panel plots these three frequencies as sine functions of time to give you another way of comparing their relative magnitudes. Note that bending vibrations are always the lowest in frequencies while antisymmetric vibrations are always the highest. Note as well that the bending vibration in CO2 is doubly degenerate; a linear triatomic can bend in either of two perpendicular planes.
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