The 5d states of barium hydride; BaH and BaD

The A′ 2 Δ, A 2 Π and B 2 Σ + states of BaH and BaD which correlate with Ba ...6s5d 3 D have been observed in infra-red laser-induced fluorescence from E 2 Π and in thermal emission to the ground state, X 2 Σ + . The spectra were recorded interferometrically using a high resolution Fourier transform spectrometer. Observations include v = 0 and 1 of the complex, both for BaH and BaD. A global analysis of these levels is given in terms of an effective hamiltonian for a d-complex. The observed interactions require a 15 × 15 representation of the complex of BaH, with the use of experimental data for v = 2 taken from the work of other authors. However an independent 5 × 5 representation of each vibrational level is shown to describe the BaD spectrum with very good accuracy, in particular the complicated local A′ 2 Δ ∼ A 2 Π perturbations. The spectra of both molecules are reproduced to within the experimental precision. Deperturbed energies and rotational constants, and values of the interaction constants are given. A consistent set of molecular constants is also reported for the X 2 Σ + and E 2 Π states of BaH and BaD, and for the perturbing level v = 5 in B 2 Σ + of BaD. A simple analysis of the interaction constants indicates that A′ 2 Δ is essentially a covalent state which correlates with Ba (6sσ5dδ), and that A 2 Π is largely, ∼ 80 per cent, covalent (6sσ5dπ). The results do not allow an estimate of the configuration of B 2 Σ + . Some rotational structure of the 0-0 bands of the forbidden systems, A′ 2 Δ-X 2 Σ + , of BaH and BaD are included in the overall fit: it is unusual in that the bands seem to be limited to only three branches, Q R 12 , P Q 12 and R Q 21 .