Dobryakov A L, Krohn O A, Quick M, Ioffe I N, Kovalenko S A
Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489 Berlin, Germany.
Department of Physics and of Chemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
J Chem Phys. 2022 Feb 28;156(8):084304. doi: 10.1063/5.0075116.
Resonance stimulated Raman signal and line shape are evaluated analytically under common electronic/vibrational dephasing and exponential Raman/probe pulse, exp(-|t|/τ). Generally, the signal from a particular state includes contributions from higher and lower electronic states. Thus, with S → S actinic excitation, the Raman signal consists of 15 Feynman diagrams entering with different signs. The negative sign indicates vibrational coherences in S or higher S, whereas the positive sign reveals coherences in S or S via S → S → S (n < m) coupling. The signal complexity is in contrast to spontaneous Raman with its single diagram only. The results are applied to femtosecond stimulated Raman spectra of trans-trans, cis-trans (ct), and cis-cis (cc) 1,4-diphenyl-1,3-butadiene, the ct and cc being reported for the first time. Upon actinic excitation, the Stokes spectra show negative bands from S or S. When approaching higher resonances S → S, some Raman bands switch their sign from negative to positive, thus, indicating new coherences in S. The results are discussed, and the measured Raman spectra are compared to the computed quantum-chemical spectra.
在常见的电子/振动退相以及指数形式的拉曼/探测脉冲exp(-|t|/τ)条件下，对共振激发拉曼信号和线形进行了分析评估。一般来说，来自特定态的信号包含来自较高和较低电子态的贡献。因此，在S→S光化激发下，拉曼信号由15个带有不同符号的费曼图组成。负号表示S态或更高S态中的振动相干性，而正号则通过S→S→S（n < m）耦合揭示S态或S态中的相干性。信号的复杂性与仅具有单个图的自发拉曼形成对比。这些结果被应用于反式-反式、顺式-反式（ct）和顺式-顺式（cc）1,4-二苯基-1,3-丁二烯的飞秒受激拉曼光谱，其中ct和cc光谱首次被报道。在光化激发下，斯托克斯光谱显示出来自S态或S态的负带。当接近更高的共振S→S时，一些拉曼带的符号从负变为正，因此表明S态中有新的相干性。对结果进行了讨论，并将测量的拉曼光谱与计算的量子化学光谱进行了比较。
