Quantum Chemistry 6.8 – Rotation-Vibration Interaction

Short lecture on rotation-vibration interaction in the rigid rotor.

The harmonic oscillator quantum mechanical model system approximates the vibrational potential energy surface of a diatomic molecule as a parabola. This approximation breaks down severely at long bond distances, as the molecule begins to dissociate. Higher vibrational energy states have greater degrees of anharmonicity as the approximation breaks down. This results in a greater bond length at higher vibrational states, thus a higher momentum of inertia, a smaller rotational constant, and more closely spaced spectral lines. This also causes smaller spacings in the R branch than the P branch in rovibrational spectroscopy.

Notes Slide: http://i.imgur.com/TGsSJvI.png

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