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The A' 2A, A 21-[ and B2• + states of BaH and BaD which correlate with Ba ... 6sSd 3D have been observed in infra-red laser-induced fluorescence from E2II and in thermal emission to the ground state, X 2Y-+. 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 x 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 x 5 representation of each vibrational level is shown to describe the BaD spectrum with very good accuracy, in particular the complicated local A' 2A ~" A 21-I 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 2E + and E 2H states of BaH and BaD, and for the perturbing level v = 5 in B 2E + of BaD. A simple analysis of the interaction constants indicates that A' 2A is essentially a covalent state which correlates with Ba (6sa5d~), and that A 2H is largely, ~ 80 per cent, covalent (6strSdr 0. The results do not allow an estimate of the configuration of B 2~ +. Some rotational structure of the 0--0 bands of the forbidden systems, A' 2A-X 2E+, 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, t2RI2 , PQ12 and RQ21.

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