Optical spectroscopy of TaH: Six low-lying electronic states and their agreement with computational studies*

We have recorded electronic spectra of tantalum hydride (TaH) over the region 605–665 nm. The spectra were recorded by laser excitation spectroscopy at Doppler-limited resolution using a continuous-wave ring dye laser. We have assigned and fitted a total of 12 different bands, which originate from one of three low-lying electronic states. Calculations by Mark Gordon’s group and previous experimental work in our group confirm that the Ω = 2 ground state is largely derived from a σ²δπ, ³Φ₂ state. An Ω = 0⁺ state, largely a mixture of ³Σ^– and ³Π, lies only 76 cm^–1 above the Ω" = 2 ground state. By recording dispersed fluorescence, we found and characterized a total of six low-lying states of the molecule. The electronic states have been fitted by least-squares using a Hund’s case (c) Hamiltonian. We report term energies, vibrational frequencies, rotational and centrifugal distortion constants, and bond lengths for these states, which were found to be in good agreement with the computational results.