Charles V. Shank

Physical Chemistry — Ultrafast dynamics of molecular vibrations and chemical reactions are studied with femtosecond optical pulses.

Professor Shank is intrigued by ultrafast processes in matter that occur on a time scale measured in femtoseconds. Recent advances in laser pulse generation and measurement techniques have opened up the possibility of experimental investigations in the femtosecond time domain. Such techniques have shown great promise for exploring a new class of problems concerning nonequilibrium phenomena in the condensed phase. In his laboratory his group is currently performing measurements which permit them to probe molecular dynamics in solution in a time short compared to a molecular vibration.

Recent work in his laboratory has included the study of dephasing of an optically excited polarization of a molecule in solution. In the past, attempts at such measurements have been frustrated by the lack of adequate time resolution. Two and three pulse photon echo experiments have been performed using 6 femtosecond optical pulses. Shank's group hopes to use these investigations to determine the role of solvent interactions and internal molecular degrees of freedom in the dephasing process.

With a sufficiently short optical pulse, it is possible to excite the entire manifold on Franck-Condon connected states for the first excited singlet for a molecule in solution. If the pulse is short compared to a vibrational period, it is possible to excite a nonstationary state which can be described by wavepacket motion on the excited and ground states of the molecule. This technique is being used to measure vibrational spectra of molecules undergoing photochemistry.