On the validity of collisional-radiative models

I derive strict conditions for the validity of the collisional-radiative (C R) models widely used in plasma physics, and show that conditions on the ei genvectors of the full matrix of rates must be satisfied and that, in contr ast to the conventional view, the eigenvalues have secondary importance. I use the results to analyse some CR models for molecular hydrogen. (C) 2001 Elsevier Science B.V. All rights reserved.