Physical Chemistry Third Edition

22

Translational, Rotational, and

Vibrational States of Atoms

and Molecules

PRINCIPAL FACTS AND IDEAS

1. Atoms have translational and electronic energy.


2. The electronic energy of atoms can usually be ignored.


3. The translational energy of an atom can be represented as that of a
   structureless particle.


4. Molecules have translational, electronic, rotational, and vibrational
   energy. The translational energy can be represented as that of a
   structureless particle.


5. The Born–Oppenheimer approximation is used to separate the electronic
   motion from the rotational and vibrational motion of molecules.


6. The Born–Oppenheimer energy acts as a potential energy for vibration.


7. In homonuclear diatomic molecules, only half of the values ofJ, the
   rotational quantum number, are permitted. In polyatomic molecules 1/σ
   of the conceivable rotational states are permitted, whereσis the
   symmetry number of the molecule.


8. The population of molecular states is governed by the Boltzmann
   probability distribution.

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