Grotrian diagram for C I in the standard model atom, after reducing the comprehensive model by removing C III and all excited levels of C II, and by constructing super levels. Levels that do not resolve fine structure are shown as red lines, and super levels are shown as long horizontal lines. Some of the C I lines explicitly considered in this work have been highlighted; “~ 711 nm” refers to the C I 711.1 and 711.3 nm lines, and “~ 960 nm” refers to the C I 960.3 and 965.8 nm lines.