**Examples: CH _{4}, CCl_{4},
SF_{6}**

For the case of I = I_{A} = I_{B} = I_{C} the
rotational energy is given by:

We obtain the respective quantum mechanical equation if we shift to the
operators **H** and **J**:

The eigenvalues to **J**² are already
known: **J**²⋅Ψ =
J(J+1) * h*²⋅Ψ with J =
0, 1, 2, ...

It has become common practice to write this equation in a form with the
** rotational constant B** which has the unit of the wavenumber,
cm

With c denoting the speed of light, the transformation between the moment of inertia I and rotational constant B is

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