Matrix Isolation Spectroscopy: Aqueous p-Toluenesulfonic Acid Solvation

Interaction between p-toluenesulfonic acid (pTSA) and water is studied at −20 °C in a CCl4 matrix. In CCl4 water exists as monomers with restricted rotational motion about its symmetry axis. Additionally, CCl4 is transparent in the hydrogen-bonded region; CCl4 thus constitutes an excellent ambient thermal energy matrix isolation medium for diagnosing interactions with water. Introducing pTSA-nH2O gives rise to two narrow resonances at 3642 cm–1 and at 2835 cm–1 plus a broad 3000–3550 cm–1 absorption. In addition, negative monomer symmetric and asymmetric stretch features relative to nominally dry CCl4 indicate that fewer water monomers exist in the cooled (−20 °C) acid solution than in room-temperature anhydrous CCl4. The negative peaks along with the broad absorption band indicate that water monomers are incorporated into clusters. The 3642 cm–1 resonance is assigned to the OH-π interaction with a cluster containing many water molecules per acid molecule. The 2835 cm–1 resonance is assigned to the (S-)O–...