Rotational analysis and assignment of the 630 nm band system of FeH to the e 6Π–c 6Σ+ transition

An investigation of the electronic spectrum of FeH at ∼630 nm using dispersed and undispersed laser induced fluorescence techniques is reported. Eighty lines have been assigned to the (0,0) vibrational band of the e 6Π–c 6Σ+ transition. The transitions can be arranged in three subbands with all six spin components of the c 6Σ+ state accessed. This has allowed the c 6Σ+ state to be fully characterized and provides parity assignments of individual rotational levels for the first time. The energy levels of the c 6Σ+ state conform approximately to a Hund’s case (a′) coupling scheme with significant Ω-type doubling (1–10 cm−1). An attempt has been made to simulate the levels using an effective Hamiltonian. Although the simulation failed to reproduce the results to within experimental uncertainty (∼0.007 cm−1), the residuals are sufficiently small to confirm the correctness of the assignments.