Matrix Isolation Spectroscopy: Aqueous p-Toluenesulfonic Acid Solvation

Area of Science:

• Physical Chemistry
• Spectroscopy
• Chemical Physics

Background:

• Carbon tetrachloride (CCl4) serves as an effective matrix isolation medium due to its transparency in the hydrogen-bonded region.
• Water molecules in CCl4 exhibit restricted rotational motion, existing primarily as monomers.

Purpose of the Study:

• To investigate the interactions between p-toluenesulfonic acid (pTSA) and water at low temperatures (-20 °C) using matrix isolation spectroscopy.
• To elucidate the structural and bonding characteristics of pTSA-water complexes in a CCl4 environment.

Main Methods:

• Matrix isolation infrared (IR) spectroscopy was employed using a CCl4 matrix at -20 °C.
• The study analyzed spectral features, including narrow resonances and broad absorption bands, to identify molecular species and interactions.

Main Results:

• The introduction of pTSA-nH2O resulted in distinct IR absorptions at 3642 cm⁻¹ and 2835 cm⁻¹, alongside a broad band from 3000-3550 cm⁻¹.
• Negative peaks for water monomer stretches indicated a decrease in free monomers, suggesting their incorporation into clusters.
• The 3642 cm⁻¹ resonance was attributed to OH-π interactions within water-rich clusters, while the 2835 cm⁻¹ resonance was assigned to the S-O-H stretch of pTSA-dihydrate.

Conclusions:

• Water monomers in the CCl4 matrix are incorporated into clusters upon interaction with pTSA.
• The study identified specific interactions, including OH-π interactions and the formation of pTSA-dihydrate, providing insights into the acid-water system.