Electronic and resonance Raman spectroscopic studies on the tetrathiomolybdate(VI) ion, [MoS4]2–. Determination of the excited-state molecular geometry

Abstract

The electronic absorption and resonance Raman spectra of the tetrathiomolybdate(VI) ion have been recorded at low temperatures on solid samples. The resonance Raman spectrum, excited within the contour of the lowest-energy charge-transfer absorption band (¹T₂â†�¹A₁) at ca. 470 nm, is characterized by a number of overtone and combination tone progressions, the most prominent being that in ν₁(a₁). A theoretical model, based on the Condon approximation and the harmonic-oscillator approximation for both the ground and excited states, is used to simulate the excitation profiles of ν₁ and its first two overtones, from which it is calculated that the MoS bond length increases by 0.07 ± 0.005 Å in the excited state. Additionally, we discuss the nature of excited-state Jahn–Teller effects and the bandwidths of the members of the v₁ν₁ progression in terms of current theoretical knowledge.