Bordenyuk Andrey N, Benderskii Alexander V
Department of Chemistry, Wayne State University, Detroit, MI 48202, USA.
J Chem Phys. 2005 Apr 1;122(13):134713. doi: 10.1063/1.1873652.
Time- and frequency-domain three-wave mixing spectroscopy (IR+visible sum frequency generation) is developed as the lowest-order nonlinear technique that is both surface selective and capable of measuring spectral evolution of vibrational coherences. Using 70 fs infrared and 40 fs visible pulses, we observe ultrafast spectral dynamics of the OD stretch of D2O at the CaF2 surface. Spectral shifts indicative of the hydrogen-bond network rearrangement occur on the 100 fs time scale, within the observation time window determined by the vibrational dephasing. By tuning the IR pulse wavelength to the blue or red side of the OD-stretch transition, we selectively monitor the dynamics of different subensembles in the distribution of the H-bond structures. The blue-side excitation (weaker H-bonding structures) shows monotonic decay and nu(OD) frequency shift to the red on a 100 fs time scale, which is better described by a Gaussian than an exponential frequency correlation function. In contrast, the red-side excitation (stronger H-bonding structures) results in a blue spectral shift and a recursion in the signal at 125+/-10 fs, indicating the presence of an underdamped intermolecular mode of interfacial water.
时域和频域三波混频光谱（红外+可见和频产生）被开发为一种最低阶非线性技术，它既具有表面选择性，又能够测量振动相干的光谱演化。使用70飞秒红外脉冲和40飞秒可见脉冲，我们观察了CaF2表面D2O的OD伸缩振动的超快光谱动力学。在由振动退相确定的观察时间窗口内，表明氢键网络重排的光谱位移在100飞秒时间尺度上发生。通过将红外脉冲波长调至OD伸缩振动跃迁的蓝侧或红侧，我们选择性地监测了氢键结构分布中不同子系综的动力学。蓝侧激发（较弱的氢键结构）在100飞秒时间尺度上呈现单调衰减，且ν(OD)频率向红移，用高斯函数比指数频率相关函数能更好地描述这种情况。相比之下，红侧激发（较强的氢键结构）导致光谱蓝移，并在125±10飞秒时信号出现递归，表明存在界面水的欠阻尼分子间模式。
