The Theorem of the Equipartition of energy is a construct of classical mechanics and was first introduced by James Clerk Maxwell (1831-1879). It states:
"Every kind of molecule has a particular number of degrees of freedom f which are independent ways in which it can store energy. Each such degree of freedom has associated with it, on average, an energy of per molecule or per mole, where k is the Boltzmann constant, R is the molar gas constant and T is temperature in kelvin.".
Degrees of freedom can be translational, rotational, or oscillatory.
- Fundamentals of Physics, Fourth Edition by David Halliday, Robert Resnick, and Jearl Walker p591