Center for Functional Materials and Nanomolecular Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany.
J Phys Chem A. 2012 Nov 26;116(46):11341-6. doi: 10.1021/jp305579t. Epub 2012 Aug 2.
In previous work (Scaria, A.; et al. Chem. Phys. Lett. 2009, 470, 39-43) it was shown that the excitation of the electronic B state in bromine can be characterized by transitions starting from vibrational hot states of the electronic ground X state. This contribution is strongly depending on the specific Franck-Condon factors for the chosen wavelength (in that work 540 nm) used for excitation. For the investigation of the resulting excited state dynamics, a pump-degenerate four-wave mixing (pump-DFWM) experiment was applied. To increase the vibrational selectivity, in the present work we have performed temperature-dependent time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy to probe the B state dynamics of bromine. Also here, the wavelength of the excitation (in this case, the pump laser of the CARS process) was set to 540 nm for all measurements. The hot state contribution is small, even at high temperatures. It can be probed by tuning the Stokes wavelength to resonance. The time delay between the probe pulse and the time-coincident pump/Stokes pulse pair of the CARS process is scanned, giving access to the wave packet dynamics in the excited B state. The experimental observations are supported by quantum dynamical calculations.
在之前的工作中（Scaria，A.；等人。化学物理快报。2009 年，470，39-43）表明，可以通过从电子基态 X 态的振动热态开始的跃迁来描述溴中电子 B 态的激发。这种贡献强烈依赖于用于激发的特定 Franck-Condon 因子（在该工作中为 540nm）。为了研究所得激发态动力学，应用了泵简并四波混频（泵-DFWM）实验。为了提高振动选择性，在本工作中，我们进行了温度相关的时间分辨相干反斯托克斯拉曼散射（CARS）光谱学研究，以探测溴的 B 态动力学。同样，在所有测量中，激发（在这种情况下，CARS 过程的泵激光）的波长均设置为 540nm。即使在高温下，热态贡献也很小。通过将斯托克斯波长调谐到共振，可以探测到它。扫描 CARS 过程中探针脉冲与时间重合的泵/斯托克斯脉冲对之间的时间延迟，可获得激发态 B 中的波包动力学。实验观察结果得到量子动力学计算的支持。
