Ambient Energy Matrix Isolation Spectroscopy: A Molecular Study of p-Toluenesulfonic Acid Solvation.
Khuu, Thien T.
- Clathrate hydrates are water cages that incase hydrophobic gases, such as methane and CO2. They form under extreme conditions (pressure ranging from 9 to several thousand atm, and at cryogenic temperature). They occur naturally in the permafrost and on the continental shelf of the seabed (700 m) where the pressure is about 70 atm. Clathrates are estimated to contain a substantial amount of energy.... read moreExtraction of this energy is dangerous and not environmentally favorable, since clathrate hydrates are not stable without its guest gas and at lower pressure environment. Careless extractions could release all the trapped hydrocarbon at once, thus accelerate global warming. Nonetheless, they have the potential to be a good system for cleaning greenhouse gases such as CO2 and as a gas storage and transfer media. To produce these gas hydrate cost-effectively, promoters, such as the hydrotrope pToluenesulfonic acid (pTSA), are used. The molecular mechanism of how promoters interact with water and the guest gas molecule is studied here using a method called Ambient Energy Matrix Isolation Spectroscopy, or AE-MIS. AE-MIS uses carbon tetrachloride (CCl4) matrix to simplify the water spectrum in the mid-IR region. The vibrational signatures of water in CCl4 – the symmetric stretch, asymmetric stretch, and rotation about the symmetry axis – are present because water exists as monomers in CCl4 with quenched rotation about the axes perpendicular to the symmetry axis. Monitoring and interpreting changes of these features when studying water interaction with other molecules can give a molecular insight to puzzling mechanisms of bigger systems. Herein, experimental spectra of small (pTSA)•(H2O)n clusters (n ≤ 10) and large clusters (n ≥ 20) are presented. Peak assignments and a proposed bimodal distribution model are aided by Density Functional Theory (DFT) calculations.read less