ABSTRACT
It is sometimes advantageous to use special units for atoms and molecules. In the system of atomic units, the unit of length is called 1 Bohr and is equal to the radius of the hydrogen atom. Other atoms are roughly the same size. The atomic unit of energy is called Hartree and is an order of magnitude larger than that of the excitation energies in the visible spectrum. The atomic unit of mass is the rest mass of the electron. Atomic units are obtained as follows:
Dene:
1. Atomic unit for action (energy × time) or moment of momentum: Planck’s constant h divided by 2pi (ħ = 1).
