Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Chem Phys. 2010 Jan 28;132(4):044501. doi: 10.1063/1.3285265.
The asymmetric stretching vibration of the amphiphilic trifluoroacetate ion and its (13)C=(16)O isotopologue in D(2)O were investigated with infrared spectroscopy (FTIR), ultrafast infrared pump probe, and two dimensional vibrational photon echo techniques and simulations. Trifluoroacetate ions have a nonexponential depopulation of the first vibrational excited state, which is well described by a kinetic mechanism involving a temperature dependent solvent assisted relaxation to the symmetric stretch mode. The vibrational spectrum of the asymmetric stretch of the (13)C=(16)O isotopologue presents an unusual spectral shape. The frequency-frequency autocorrelation function shows a static term not present in the (13)C=(16)O form, which is caused by an accidental degeneracy with a combinational mode. A newly developed frequency map for carboxylate is used to characterize the processes and dynamics observed in the frequency fluctuations of the carboxylate asymmetric stretch mode in aqueous solution. An assignment of the molecular processes that govern the frequency fluctuations is suggested from an analysis of the solvation shell configurations obtained from molecular dynamics simulations.
采用红外光谱（FTIR）、超快红外泵浦探针和二维振动光子回波技术及模拟方法，研究了两性三氟乙酸离子及其（13）C=（16）O 同位素在 D（2）O 中的不对称伸缩振动。三氟乙酸离子的第一振动激发态的非指数去激发，很好地用一个动力学机制来描述，该机制涉及到一个依赖于温度的溶剂辅助弛豫到对称伸缩模式。（13）C=（16）O 同位素的不对称伸缩的振动光谱呈现出一种不寻常的光谱形状。频率-频率自相关函数显示出一个在（13）C=（16）O 形式中不存在的静态项，这是由与组合模式的偶然简并引起的。一个新开发的羧酸酯频域图用于描述水溶液中羧酸酯不对称伸缩模式的频率波动中观察到的过程和动力学。从分子动力学模拟获得的溶剂化壳结构的分析中，提出了控制频率波动的分子过程的分配。
