Absorption Spectrum of Hydroperoxymethyl Thioformate: A Computational Chemistry Study

Area of Science:

• Atmospheric chemistry
• Marine sulfur cycling
• Photochemistry

Background:

• Hydroperoxymethyl thioformate (HPMTF) is a sulfur compound significant in marine atmospheric chemistry.
• Its atmospheric chemical cycling is poorly understood due to limited knowledge of its photolytic behavior.
• Previous studies relied on chromophore approximations for HPMTF photolysis rates.

Purpose of the Study:

• To accurately calculate the absorption spectra of HPMTF in gas and aqueous phases.
• To determine reliable photolysis rates for HPMTF.
• To compare computational results with previous approximations.

Main Methods:

• Utilized the Nuclear Ensemble Approach (NEA) for calculations.
• Employed the Complete Active Space Perturbation Theory to second order (CASPT2) method.
• Calculated absorption spectra and relative photolysis rates in both gas and aqueous phases.

Main Results:

• The chromophore approximation overestimates gas-phase photolysis rates by a factor of two compared to NEA-CASPT2.
• Calculated absorption spectra for HPMTF in gas and aqueous environments.
• Predicted a reduced role for photolysis in the aqueous phase relative to the gas phase.

Conclusions:

• The study provides accurate photolysis rates for HPMTF, improving atmospheric models.
• NEA-CASPT2 method offers a more reliable approach than chromophore approximations.
• Photolysis plays a lesser role in the aqueous phase for HPMTF compared to the gas phase.