Quantum molecular motion in the mixed ion-radical complex, [(H₂O)(H₂S)]

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• The water and hydrogen sulfide cation dimer, [(H2O)(H2S)]+, is a key model for H2S oxidation chemistry.
• Biological oxidation of H2S in sulfur-rich environments motivates studying this complex.
• Its properties may inform water oxidation chemistry mechanisms.

Purpose of the Study:

• To investigate the quantum molecular motion of the [(H2O)(H2S)]+ cation.
• To understand deviations from classical and harmonic analyses in this radical cation.
• To explore implications for oxidation chemistry and vibrational spectroscopy.

Main Methods:

• Path integral molecular dynamics simulations.
• Anharmonic vibrational spectroscopy simulations.
• Analysis of structural distributions and vibrational spectra.

Main Results:

• Observed significant deviations from classical and harmonic analyses.
• Identified large-amplitude anharmonic motion of the central proton.
• Detected nearly free rotation of terminal hydrogens.

Conclusions:

• The [(H2O)(H2S)]+ cation displays unique quantum behavior, including anharmonic proton motion and hydrogen rotation.
• Predicted vibrational spectra show characteristic signatures of strong electronic interactions and anharmonic couplings.
• The complex's intermediate character between known regimes leads to novel molecular dynamics.