Ultrafast Conversions Between Hydrogen Bonded Structures in Liquid Water Observed by Femtosecond X-Ray Spectroscopy.

Wen, H. ; Huse, N. ; Schoenlein, R. W. ; Lindenberg, A. M.

Technical Information Center Oak Ridge Tennessee

关键词: Water;    Hydrogen;    Chemical bonds;    X-ray spectroscopy;    Molecules;   

RP-ID  :  DE2010983224

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

We present the first femtosecond soft x-ray spectroscopy in liquids, enabling the observation of changes in hydrogen bond structures in water via core-hole excitation. The oxygen K-edge of vibrationally excited water is probed with femtosecond soft x-ray pulses, exploiting the relation between different water structures and distinct x-ray spectral features. After excitation of the intramolecular OH stretching vibration, characteristic x-ray absorption changes monitor the conversion of strongly hydrogen-bonded water structures to more disordered structures with weaker hydrogen-bonding described by a single subpicosecond time constant. The latter describes the thermalization time of vibrational excitations and defines the characteristic maximum rate with which nonequilibrium populations of more strongly hydrogen-bonded water structures convert to less-bonded ones. On short time scales, the relaxation of vibrational excitations leads to a transient high-pressure state and a transient absorption spectrum different from that of statically heated water.