Shim Sangdeok, Mathies Richard A
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2008 Apr 17;112(15):4826-32. doi: 10.1021/jp710518y. Epub 2008 Mar 26.
We have developed a tunable femtosecond stimulated Raman spectroscopy (FSRS) apparatus and used it to perform time-resolved resonance Raman experiments with <100 fs temporal and <35 cm(-1) spectral resolution. The key technical change that facilitates this advance is the use of a tunable narrow-bandwidth optical parametric amplifier (NB-OPA) presented recently by Shim et al. (Shim, S.; Mathies, R. A. Appl. Phys. Lett. 2006, 89, 121124). The practicality of tunable FSRS is demonstrated by examining the photophysical dynamics of beta-carotene. Using 560 nm Raman excitation, the resonant S1 state modes are enhanced by a factor of approximately 200 compared with 800 nm FSRS experiments. The improved signal-to-noise ratios facilitate the measurement of definitive time constants for beta-carotene dynamics including the 180 fs appearance of the S1 vibrational features due to direct internal conversion from S2 and their characteristic 9 ps decay to S0. By tuning the FSRS system to 590 nm Raman excitation, we are able to selectively enhance vibrational features of the hot ground state S hot 0 and monitor its approximately 5 ps cooling dynamics. This tunable FSRS system is valuable because it facilitates the direct observation of structural changes of selected resonantly enhanced states and intermediates during photochemical and photobiological reactions.
我们开发了一种可调谐飞秒受激拉曼光谱（FSRS）装置，并使用它进行了时间分辨共振拉曼实验，其时间分辨率小于100飞秒，光谱分辨率小于35厘米⁻¹。促成这一进展的关键技术改进是采用了Shim等人（Shim, S.; Mathies, R. A. Appl. Phys. Lett. 2006, 89, 121124）最近提出的可调谐窄带宽光学参量放大器（NB - OPA）。通过研究β - 胡萝卜素的光物理动力学，证明了可调谐FSRS的实用性。使用560纳米拉曼激发时，与800纳米FSRS实验相比，共振S1态模式增强了约200倍。改进的信噪比有助于测量β - 胡萝卜素动力学的确定时间常数，包括由于从S2直接内转换导致的S1振动特征的180飞秒出现及其向S0的9皮秒特征衰减。通过将FSRS系统调谐到590纳米拉曼激发，我们能够选择性地增强热基态S热0的振动特征，并监测其约5皮秒的冷却动力学。这种可调谐FSRS系统很有价值，因为它有助于在光化学和光生物学反应过程中直接观察选定的共振增强态和中间体的结构变化。
