Femtosecond Laser Studies of

Molecules at Liquid Surfaces

by

Kenneth B. Eisenthal

Columbia University

The combination of femtosecond laser methods and nonlinear optical spectroscopy makes it possible to probe ultrafast molecular motions at liquid interfaces. In one study the motion of solvent molecules surrounding a solute molecule is obtained by photoexciting the interfacial solute molecules with a femtosecond laser pulse and following the time evolution of the photoexcited molecules. This process, called solvation dynamics, is important in understanding fast chemical reactions, such as electron and proton transfer. In another study the rotational motion of interfacial solute molecules is measured by perturbing their orientation of distribution with a femtosecond laser pulse. The dynamics of this motion provides a measure of the molecular friction at the liquid interface.