Raman characterization for vibrations of aqueous methanediol and its oligomers

Area of Science:

• Atmospheric Chemistry
• Spectroscopy
• Chemical Physics

Background:

• Methanediol and its oligomers are crucial in atmospheric multiphase chemistry.
• Spectroscopic characterization of these species in aqueous solutions is limited.
• Understanding these species is key to atmospheric modeling.

Purpose of the Study:

• To characterize methanediol and its oligomers (n=1-3) in aqueous solutions using Raman spectroscopy.
• To assign specific Raman spectral features to monomer, dimer, and trimer species.
• To elucidate the role of these species in atmospheric formaldehyde chemistry.

Main Methods:

• Aqueous solutions of formaldehyde were analyzed using Raman spectroscopy.
• Spectral decomposition was employed to isolate individual spectra of methanediol monomer, dimer, and trimer.
• Density functional theory (DFT) calculations were used for spectral assignment.

Main Results:

• Oligomers (dimer, trimer) show characteristic COC stretching bands at 921 cm⁻¹ and 1121 cm⁻¹, and a CH₂ rocking mode near 1319 cm⁻¹.
• The trimer exhibits an additional COC stretching band near 937 cm⁻¹.
• The OCO stretching band shifts from 1048 cm⁻¹ (monomer) to 1063 cm⁻¹ (oligomers).

Conclusions:

• Raman spectroscopy successfully differentiated methanediol monomer from its dimer and trimer.
• Specific vibrational modes provide unique fingerprints for identifying these species.
• This work enhances the understanding of formaldehyde's role in atmospheric chemistry.