Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
J Chem Phys. 2011 Jan 14;134(2):024307. doi: 10.1063/1.3525100.
We present a quantum mechanical wave packet treatment of time-resolved femtosecond stimulated Raman spectroscopy (FSRS), or two-dimensional (2D) FSRS, where a vibrational coherence is initiated with an impulsive Raman pump which is subsequently probed by FSRS. It complements the recent classical treatment by Mehlenbacher et al. [J. Chem. Phys. 131, 244512 (2009)]. In this 2D-FSRS, two processes can occur concurrently but with different intensities: a direct fifth-order process taking place on one molecule, and a cascade process comprising two third-order processes on two different molecules. The cascade process comprises a parallel and a sequential cascade. The theory is applied to the 2D-FSRS of CDCl(3) where calculations showed that: (a) the cascade process is stronger than the direct fifth-order process by one order of magnitude, (b) the sidebands assigned to C-Cl E and A(1) bends, observed on both sides of the Stokes C-D stretch frequency, are not due to anharmonic coupling between the C-D stretch and the C-Cl bends, but are instead due to the coherent anti-Stokes Raman spectroscopy (CARS) and coherent Stokes Raman spectroscopy (CSRS) fields produced in the first step of the cascade process, (c) for each delay time between the femtosecond impulsive pump and FSRS probe pulses, the line shape of the sidebands shows an inversion symmetry about the C-D stretch frequency, and this is due to the 180(∘) phase difference between the CARS and CSRS fields that produced the left and right sidebands, and (d) for each sideband, the line shape changes from positive Lorentzian to dispersive to negative Lorentzian, then to negative dispersive and back to positive Lorentzian with the period of the bending vibration, and it is correlated with the momentum of the wave packet prepared on the ground-state surface by the impulsive pump along the sideband normal coordinate.
我们提出了一种量子力学波包处理方法，用于时间分辨飞秒受激拉曼光谱（FSRS）或二维（2D）FSRS，其中振动相干性通过脉冲拉曼泵激发，随后用 FSRS 探测。它补充了 Mehlenbacher 等人的最近的经典处理[J. Chem. Phys. 131, 244512 (2009)]。在这种 2D-FSRS 中，两个过程可以同时发生，但强度不同：一个是在一个分子上发生的直接五阶过程，另一个是由两个不同分子上的两个三阶过程组成的级联过程。级联过程包括平行级联和顺序级联。该理论应用于 CDCl(3)的 2D-FSRS，计算表明：(a) 级联过程比直接五阶过程强一个数量级，(b) 在斯托克斯 C-D 伸缩频率的两侧观察到的分配给 C-Cl E 和 A(1)弯曲的边带，不是由于 C-D 伸缩和 C-Cl 弯曲之间的非谐耦合，而是由于在级联过程的第一步中产生的相干反斯托克斯拉曼光谱（CARS）和相干斯托克斯拉曼光谱（CSRS）场，(c) 对于飞秒脉冲泵和 FSRS 探测脉冲之间的每个延迟时间，边带的线形状在 C-D 伸缩频率处具有反转对称性，这是由于产生左右边带的 CARS 和 CSRS 场之间的 180(∘) 相位差，(d) 对于每个边带，线形状从正洛伦兹形变为色散形，再变为负洛伦兹形，然后再变为负色散形，然后再回到正洛伦兹形，其周期与沿边带法线坐标由脉冲泵在基态表面上准备的波包的动量相关。
