A semiclassical model is used to investigate the possibility of selectively exciting one of two closely spaced, uncoupled Raman transitions. The duration of the intense pump pulse that creates the Raman coherence is shorter than the vibrational period of a molecule (impulsive regime of interaction). Pulse shapes are found that provide either enhancement or suppression of particular vibrational excitations.
In Impulsive Stimulated Raman Scattering vibrational oscillations, coherently stimulated by a femtosecond Raman pulse, are real time monitored and read out as intensity modulations in the transmission of a temporally delayed probe pulse. Critically, in order to retrieve broadband Raman spectra, a fine sampling of the time delays between the Raman and probe pulses is required, making conventional ISRS ineffective for probing irreversible phenomena and/or weak scatterers typically demanding long acquisition times, with signal to noise ratios that crucially depend on the pulse fluences and overla…
Photophysical and photochemical processes are ruled by the interplay between transient vibrational and electronic degrees of freedom, which are ultimately determined by the multidimensional potential energy surfaces (PESs). Differences between ground and excited PESs are encoded in the relative intensities of resonant Raman bands, but they are experimentally challenging to access requiring measurements at multiple wavelengths under identical conditions. Here we perform a two-color impulsive vibrational scattering experiment to launch nuclear wavepacket motions by an impulsive pump and record t…
We show that (near-)zero energy proton emission from H$_2^+$ in strong two-color and broadband laser fields is dominated by a stimulated Raman scattering process taking place on the electronic ground state. It is furthermore shown that in the (near-)zero energy region the asymmetry in proton ejection induced by asymmetric laser fields is due to the interplay of several processes, rather than only pathway interferences, with vibrational trapping (or bond-hardening) taking a key role.
Iron-sulfur complexes play an important role in biological processes such as metabolic electron transport. A detailed understanding of the mechanism of long range electron transfer requires knowledge of the electronic structure of the complexes, which has traditionally been challenging to obtain, either by theory or by experiment, but the situation has begun to change with advances in quantum chemical methods and intense free electron laser light sources. We compute the signals from stimulated X-ray Raman spectroscopy (SXRS) and absorption spectroscopy of homovalent and mixed-valence [2Fe-2S] …
Excited-state vibrations are crucial for determining photophysical and photochemical properties of molecular compounds. Stimulated Raman scattering can coherently stimulate and probe molecular vibrations with optical pulses, but it is generally restricted to ground state properties. Working in resonance conditions, indeed, enables cross-section enhancement and selective excitation to a targeted electronic level, but is hampered by an increased signal complexity due to the presence of overlapping spectral contributions. Here, we show how detailed information on ground and excited state vibratio…
Valence excitation of NO$_2$ by impulsive stimulated x-ray Raman scattering
用多组态时间依赖性Hartree-Fock方法，一种完全相关的第一性原理处理方法，允许分子中每个电子的电离，确定了NO $_2$分子中由脉冲X射线受激拉曼散射驱动的价态布居转移的全局最优值。在固定核，非相对论近似计算的最终价态布居报告作为中心波长和强度的函数。的收敛性的计算相对于其可调参数进行了充分的测试。当脉冲宽度为1fs，中心频率和强度不变，无啁啾时，在强度为3.16 $\times$ 10 $^{17}$ W cm $^{-2}$，中心频率偏离二阶最佳值约6 eV的情况下，取向平均的最大布居转移率为0.7%，在一个特定取向上的最大布居转移率为2.39%.接近全局最佳值的行为，低于氧K边缘，是一致的非共振拉曼跃迁的机制驱动的近边缘精细结构振子强度。
