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