Vibrational Spectroscopy of Diatomic and Linear Molecules

For infrared absorption spectroscopy of diatomic molecules, only heteronuclear diatomic molecules show a vibrational spectrum. Their spectra are relatively simple, because there is only one vibration the motion of the two atoms back and forth about their center of mass. This is a good example of a stretching vibrational mode. Table 14.4 lists, among other data, the stretching vibrations for a series of gaseous diatomic molecules. 

Therefore, the larger the force constant, the narrower the potential energy curve. 

TABLE 14.4 Vibrational parameters of various heteronuclear diatomic molecules  

FIGURE 14.27 For an ideal harmonic oscillator, the potential energy equals and the quantized energy levels are equally spaced. 

FIGURE 14.28 A more realistic potential energy surface for the vibration of a molecule is superimposed on the ideal harmonic oscillator curve. Only at low vibrational quantum numbers does the ideal potential energy curve adequately approximate the real system. Note how the vibrational energy levels get closer and closer together as the vibrational quantum number increases. 

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