Energy level diagram of H₃⁺. The gray shaded area marks the v₂ = 1 levels. Ortho-H₃⁺ levels are in green and para-H₃⁺ in black. The metastable and ground rotational levels are indicated by thicker lines. For the ground state, the quantum numbers of each level are (J, K) and for the v₂ = 1 levels, (J,G,K). The detected transitions connect the ground and the v₂ = 1 states. The arrows show how the (3,0) level can be populated by IR pumping through the R(1,0) and P(3,0) transitions.