Vibrational Spectra.

 Vibrational Spectra;

The selection rule followed by vibration transition is ∆𝛎 = ± 1 (+ve is for absorption and -ve is for emission). The energy of vibration transition from lower level denoted by 𝛎 to upper level denoted by (𝛎+1) is given by

Transition rule for vibrational spectra.

 

Thus the pure vibrational Spectra will consist of single line as shown in fig. The frequency of spectral line is equal to classical frequency and is independent of vibrational quantum number i.e 𝛎.

Pure vibrational Spectra.

The homonuclear diatomic molecule such as H₂ ,O₂ ,N₂ have zero dipole moment, thus does not exhibit vibrational spectra, while the heteronuclear diatomic molecule such as HCl, HBr, HF, HCN etc have dipole moment, thus exhibit vibrational spectra.