How Fissors Works: Observing Vibrationally Adiabatic Conformational Change through Femtosecond Stimulated Raman Spectroscopy
How Fissors Works: Observing Vibrationally Adiabatic Conformational Change through Femtosecond Stimulated Raman Spectroscopy
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DOI：
10.1021/jp312878t
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发表时间：
2013-07-25
影响因子：
2.9
通讯作者：
Kovac, Philip A.
中科院分区：
文献类型：
--
作者：
Cina, Jeffrey A.;Kovac, Philip A.
借助一个包含慢构象自由度和高频振动的二维模型系统，我们研究了飞秒受激拉曼光谱信号的分子水平起源和动态信息含量。我们的处理利用了构象模式和振动模式之间的时间尺度分离，将振动绝热近似纳入构象动力学。我们推导了一个裂变信号的表达式，而不依赖于先前耦合波分析中使用的光波和声子波传播的宏观概念。裂变谱的数值计算说明了相对较小的构象质量（仍然足够大，构象运动不会引起振动量子数的任何变化）的情况，其中构象边带在构象平均振动跃迁频率处伴随拉曼增益的中心峰值。在更大构象质量的情况下，边带与中心峰合并，后者的频率跟踪随时间变化的构象坐标。
With the help of a two-dimensional model system comprising a slow conformational degree of freedom and a higher-frequency vibration, we investigate the molecular-level origin and dynamical information content of femtosecond stimulated Raman spectroscopy (fissors) signals. Our treatment avails itself of the time scale separation between conformational and vibrational modes by incorporating a vibrationally adiabatic approximation to the conformational dynamics. We derive an expression for the fissors signal without resort to the macroscopic concepts of light- and phonon-wave propagation employed in prior coupled-wave analyses. Numerical calculations of fissors spectra illustrate the case of relatively small conformational mass (still large enough that conformational motion does not induce any change in the vibrational quantum number) in which conformational sidebands accompany a central peak in the Raman gain at a conformationally averaged vibrational transition frequency, and the case of a larger conformational mass in which the sidebands merge with the central peak and the frequency of the latter tracks the time-evolving conformational coordinate.