CR-Model (Collision-Radiative model) is one of population model of any element (atom, ion, molecule, etc). The time evaluation of population of p-state can expressed by electron impact excitation/de-excitation, ionization, spontaneous emission, and recombination from ionization stage. Therefore, the derivative of population of p-state is

In quasi steady state (QSS)

Population of p-state is expressed by

R0 : recombining plasma component
R1 : ionizing plasma component