sentences:  The first two excited states that are relatively close in energy are a singlet (1"D"2) and singlet diradical (1"S"0).The non-radical state of atomic carbon is systematically named λ2-methylidene, and the diradical states that include the ground state is named carbon(2•) or λ2-methanediyl.The 1"D"2 and 1"S"0 states lie 121.9 kJ mol−1 and 259.0 kJ mol−1 above the ground state, respectively.