On the Analysis of Reversible Light-Induced Changes in Molecular Crystals
On the Analysis of Reversible Light-Induced Changes in Molecular Crystals
复制标题
分子晶体中光致可逆变化的分析
DOI：
10.1107/s0021889897007802
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
P. Coppens
中科院分区：
文献类型：
--
作者：
Y. Ozawa;M. Pressprich;P. Coppens
在40 K下对[RhBr 2（pyridine-d5）]Br的2.44 ms寿命激发态进行了研究，测试了新的光晶体学和低温技术。使用一种调制方法，其中激光束被具有预选频率的机械斩波器中断，并且衍射的X射线束与斩波器相位同步地被选通。响应比η的Wilson型图（定义为η hkl = [Ion（hkl）-Ioff（hkl）]/Ioff（hkl））给出了在40 K下激光照射晶体时温度升高很小（~ 12 K）的证据。当斩波器频率从20 Hz增加到40 Hz再到80 Hz时，温度变化减小，表明在激光器开启期间温度逐渐增加。用实验响应比作为观测值，用最小二乘法对激发态参数进行了修正，并用46个η实验值进行了描述和应用。尽管有迹象表明Rh-Br键在激发时会缩短，但当前的数据集太有限，无法明确确定激发后的几何变化;因此，所提出的研究主要是对新技术的开发和测试的描述。
New photocrystallographic and cryogenic techniques are tested in a 40 K study of the 2.44 ms lifetime excited state of [RhBr2(pyridine-d5)]Br. A modulation method is used in which a laser beam is interrupted by a mechanical chopper with a preselected frequency and the diffracted X-ray beam gated in synchronization with the chopper phase. Wilson-type plots of the response ratio η, defined as η hkl = [I on (hkl) - I off (hkl)]/I off (hkl), give evidence of a small (≃ 2 K) temperature increase upon laser irradiation of the crystal at 40 K. The temperature change decreases when the chopper frequency is increased from 20 to 40 to 80 Hz, pointing to a gradual temperature increase during the laser-on period. A least-squares method for the refinement of excited-state parameters, with the experimental response ratios as observations, is described and applied using 46 experimental values of η. Although there is an indication that the Rh-Br bonds are shortened on excitation, the current data-set is too limited to allow unequivocal determination of the geometry changes upon excitation; the study presented is therefore primarily a description of the development and testing of new techniques.