Transition rates and transition rate diagrams in atomic emission spectroscopy: A review

•Radiative deexcitation is a major deexcitation process in some plasmas.•Rates of radiative transitions can be presented in transition rate diagrams.•Transition rate diagrams can be calculated based on emission spectra.•Transition rate diagrams can indicate collisional excitation processes.•Transition rate diagrams of Fe II, Cu II, Mn II in a glow discharge plasma are reviewed.

In low pressure plasmas with low electron densities, such as glow discharges, radiative de-excitation is a major de-excitation process of most excited states. Their relative de-excitation rates can be determined by emission spectroscopy, making it possible to study excitation processes in these discharges. This is in contrast to denser plasmas, in which such considerations are usually based on relative populations of excited states and concepts related to thermodynamic equilibrium. In the approach using reaction rates rather than populations, a convenient tool is the recently introduced formalism of transition rate diagrams. This formalism is reviewed, its relevance to different plasmas is discussed and some recent results on glow discharge excitation of manganese, copper and iron ions are presented. The prospects for the use of this formalism for the comparison of rate constants and cross sections for charge transfer reactions with argon ions of elements of interest in analytical glow discharge spectroscopy are discussed.