期刊
JOURNAL OF CHEMICAL PHYSICS
卷 131, 期 23, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3273204
关键词
high-pressure effects; high-speed optical techniques; hydrogen bonds; liquid structure; water; X-ray absorption spectra
资金
- Office of Science, Office of Basic Energy Sciences, the Chemical Sciences, Geosciences, and Biosciences Division [DE-AC02-05CH11231]
- Department of Energy through the Stanford PULSE Institute
- National Science Foundation (NSF) [CHE-0518637]
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.
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