Time-resolved X-ray absorption spectroscopy of infrared-laser-induced temperature jumps in liquid water

Abstract

A time-resolved X-ray absorption study of the structural dynamics of liquid water on a picosecond timescale is presented. We apply femtosecond midinfrared pulses to resonantly excite the intramolecular O–H stretching band of liquid water and monitor the transient response in the oxygen K-edge absorption spectrum with picosecond X-ray pulses. In this way, structural changes in the hydrogen bond network of liquid water upon an ultrafast temperature jump of approximately 20 K are investigated. The changes of the X-ray absorption as induced by such a temperature jump are about 3.2%. This demonstrates that our method serves as a sensitive probe of transient structural changes in liquid water and that combined infrared-laser–synchrotron experiments with substantially shorter X-ray pulses, such as generated with a femtosecond slicing scheme, are possible.