Optical and calorimetric studies on the role of lattice mode softening in assisting a thermally enhanced solid state reaction

The concept of phonon-assisted solid-state chemical reactions is analyzed in the case of the thermal rearrangement of methyl p-dimethylaminobenzenesulfonate (MSE) to a zwitterionic product p-trimethylammoniumbenzenesulfonate. The experimental Raman scattering reinvestigation of MSE as a function of temperature shows that mode softening does not play an important role in the thermal reaction of MSE. A series of structural phase transitions in the [90–300 K] temperature range is shown in the MSE crystal by calorimetry, infrared absorption and Raman scattering.