Spectroscopic and theoretical investigations of ThS and ThS+

Gas-phase ThS has been produced via the reaction of laser ablated Th with H2S. Rotationally resolved electronic spectra were recorded by laser-induced fluorescence (LIF) over the range 17500-24000 cm(-1). Resonance-enhanced multiphoton ionization was used in conjunction with a time-of-flight mass spectrometer to confirm the assignments of nine LIF bands to ThS. Using excitation of a ThS band centered at 22118 cm(-1), a dispersed fluorescence spectrum revealed a vibrational progression of the X(1)Σ(+) ground electronic state and the term energies of two low-lying excited states ((3)Δ1 and (3)Δ2). Two-color photoionization spectroscopy was used to study ThS(+). An accurate ionization energy for ThS was obtained (54425(3) cm(-1)); ThS(+) vibronic term energies up to v = 7 in the X(2)Σ(+) ground state and v = 3 in the (2)Δ3/2 first excited state were recorded. High-level electronic structure calculations, with inclusion of the spin-orbit interactions yielded predictions that were in good agreement with the experimental data for ThS and ThS(+). The spectroscopic properties of ThS/ThS(+) are compared with those of the valence isoelectronic pairs ThO/ThO(+), HfO/HfO(+), and HfS/HfS(+).