MPGMC · Ultrafast dynamics of chemical reactions in solution

The field of gas-phase reaction dynamics is well developed, facilitated by a vast array of sophisticated experimental and theoretical techniques. Gas-phase studies have proved vital for developing our understanding of chemical reactivity, but most reactions in nature and practical chemical synthesis occur in the liquid phase. Reaction dynamics in the liquid phase are far less understood, but recent improvements in ultrafast laser technology now make the kinds of time-dependent study required to probe such dynamics possible. Interactions with solvent molecules may, for example, alter the relative energies of reactants and products, or affect the stability of intermediate structures, and dampen their motion through solvent friction. MPGMC seeks to quantify such effects, and establish ‘rules’ that describe the effects of solvent on a chemical reaction by comparative studies in the gas and liquid phases. The Bristol group has acquired a state-of-the art, ultrafast laser system for probing liquid phase reactions in real time using transient pump/probe IR and UV spectrometry. Photodissociative and bimolecular reactions will be studied, in a range of solvents, and the results compared to those from previous and on-going gas-phase studies of the same reactions. By observing the evolving electronic state populations (in the parent and products), and/or active vibrational modes in the products, mode-specific dynamics can be extracted and conclusions drawn about the transition state structure and the solvent’s effect on the reaction-path. The time-dependence of the absorption spectra also provides insights into the way product internal motions couple to the degrees of freedom of the solvent bath (distinguishing, for example, interactions within the initial solvent cage and those occurring after the products diffuse into the bulk solvent). In this way, MPGMC seeks to provide a molecular level understanding of the effect of solvent on reaction mechanisms.""