Exploring flat multi-minima potential energy surface by matrix isolation IR spectroscopy: Revisiting methanol-H2S...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• The methanol-H2S binary complex exhibits multiple stable conformers.
• Understanding these conformers is crucial for molecular interactions and spectroscopy.

Purpose of the Study:

• To extensively search the potential energy surface of the methanol-H2S complex.
• To experimentally identify all stable conformers in matrix isolation.
• To investigate the influence of matrix environments on conformational dynamics.

Main Methods:

• Extensive potential energy surface search using quantum chemical calculations.
• Experimental identification via infrared spectroscopy in cold argon and nitrogen matrices.
• Modeling matrix effects using a face-centered cubic lattice model.

Main Results:

• Four distinct methanol-H2S conformers were identified within a narrow energy range (-2.9 to -3.3 kcal mol-1).
• Conformers are interconvertible with low rotational barriers (<0.5 kcal mol-1) in the gas phase.
• Experimental evidence confirmed all four conformers in solid matrices, unlike previous molecular beam studies.
• Calculations showed increased rotational barriers (>1.5 kcal mol-1) within a modeled argon matrix.
• Matrix effects were found to significantly slow down conformational interconversions, trapping local minima.

Conclusions:

• The study successfully identified and characterized four methanol-H2S conformers.
• Matrix isolation significantly alters conformational dynamics compared to the gas phase.
• Computational modeling accurately predicts experimental observations of trapped conformers in solid matrices.