Molybdenum-Sulfur Bond: Electronic Structure of Low-Lying States of MoS

The molybdenum-sulfur bond plays an important role in many processes such as nitrogen-fixation, and it is found as a building block in layered materials such as MoS₂, known for its various shapes and morphologies. Here, we present an accurate theoretical and experimental investigation of the chemical bonding and the electronic structure of 20 low-lying states of the MoS molecule. Multireference and coupled cluster methodologies, namely, MRCISD, MRCISD + Q, RCCSD(T), and RCCSD[T], were employed in conjunction with basis sets up to aug-cc-pwCV5Z-PP/aug-cc-pwCV5Z for the study of these states. We note the significance of including the inner 4s²4p⁶ electrons of Mo and 2s²2p⁶ of S in the correlated space to obtain accurate results. Experimentally, the predissociation threshold of MoS was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the bond dissociation energy. Our extrapolated computational D₀ value for the ground state is 3.936 eV, in excellent agreement with our experimental measurement of 3.932 ± 0.004 eV. The largest calculated adiabatic D₀ (5.74 eV) and the largest dipole moment (6.50 D) were found for the ⁵Σ⁺ state, where a triple bond is formed. Finally, the connection of the chemical bonding of the isolated MoS species to the relevant solid, MoS₂, is emphasized. The low-lying septet states of the diatomic molecule are involved in the material as a building block, explaining the stability and the variety of the shapes and morphologies of the material.