期刊
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES
卷 66, 期 -, 页码 252-260出版社
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S0108767309054993
关键词
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资金
- EU [HPRICT-1999-50004, FP6-503641]
- Creative Research Initiative (Centre for Time-Resolved Diffraction, Kaist) of MEST/NRF
- Ministry of Education, Science & Technology (MoST), Republic of Korea [KIOST, R31-2008-000-10071-0] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
- National Research Foundation of Korea [2007-0054844] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
A time-resolved X-ray solution scattering study of bromine molecules in CCl4 is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100 ps to 10 mu s after dissociation. The relaxation of hot Br-2* molecules heats the solvent. At early times, from 0.1 to 10 ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10 ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br-2* molecules recombine directly along the X potential, 60% are trapped in the A/A' state with a lifetime of 5.5 ns, and 10% recombine non-geminately via diffusive motion in about 25 ns. The Br-Br distance distribution in the A/A' state peaks at 3.0 angstrom.
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