According to the vector model of atoms, the orbital angular momentum coupling of L and S in ls coupling is L= 1. When the spin angular momentum is coupled, S = 1, 0. The multiple spectral terms of atoms are determined by various possible S and L values, and the energy differences between different spectral terms are quite large.

In mathematical concept, vector is also called vector, which refers to a directional quantity. In physical concept, it refers to physical quantities that need magnitude and direction to be fully expressed, including displacement, velocity, acceleration, force, moment, momentum and impulse.