(a) The water molecule has three distinguishable molecular vibrations. Construct a diagram like Fig. 12.8 for the three vibrational modes of water.

(b) Classify each vibration as a stretching or bending vibration.

(c) The IR spectrum of water vapor has three absorptions: 1595, 3652, and 3756 cm^–1. Which are stretching vibrations and which are bending vibrations? Explain.

Transcribed Image Text:

FIGURE 12.8 Normal vibra- tional modes of a typical CH₂ group in a structure R-CH₂-R. In each model, the white spheres are the hydrogens, the black sphere is the carbon of the CH₂, and the blue spheres represent the R groups. The center model in each normal mode represents the average position of the hydrogens. For each mode, start at the center and view left, center, right, center to see how the hydrogens move with time. average position time symmetrical stretch unsymmetrical stretch unsymmetrical in-plane bend (rock) symmetrical in-plane bend (scissor) symmetrical out-of-plane bend (wag) unsymmetrical out-of-plane bend (twist)