Rotational temperature
The characteristic rotational temperature is commonly used in statistical thermodynamics to simplify the expression of the rotational partition function and the rotational contribution to molecular thermodynamic properties. It has units of temperature and is defined as
where is the rotational constant, is a molecular moment of inertia, is the Planck constant, is the speed of light, is the reduced Planck constant and is the Boltzmann constant.
The physical meaning of is as an estimate of the temperature at which thermal energy is comparable to the spacing between rotational energy levels. At about this temperature the population of excited rotational levels becomes important. Some typical values are given in the table. In each case the value refers to the most common isotopic species.
