Characterizing dissociative motion in time-resolved x-ray scattering from gas-phase diatomic molecules
Characterizing dissociative motion in time-resolved x-ray scattering from gas-phase diatomic molecules
复制标题
表征气相双原子分子的时间分辨 X 射线散射中的解离运动
DOI：
10.1103/physreva.100.033413
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发表时间：
2019
影响因子：
2.9
通讯作者：
P. Bucksbaum
中科院分区：
文献类型：
--
作者：
Matthew R. Ware;J. Glownia;Noor Al;J. O’Neal;P. Bucksbaum
时间分辨 X 射线散射 (TRXS) 可测量激光诱导光激发后分子中的核间分离。由激发激光引起的分子动力学可以位于一种或多种束缚或离解电子态上。来自这些状态的 TRXS 可能很难隔离，因为它们通常在角度分辨 X 射线散射图案 $I(x,y,{\tau})$ 中重叠，其中 ${\tau}$ 是泵浦探针延迟，$x,y$ 是物理像素位置。在这里，我们展示了标准变换方法如何将动态与各个状态隔离。我们形成时间傅立叶变换$\tilde{I}(x,y,{\omega})$$=\int_{-\infty}^{\infty} d\tau e^{-i\omega\tau} I(x,y,\tau)$。该频率分辨 X 射线散射 (FRXS) 信号根据振动频率 ${\omega}_i$ 分离束缚态，并且还沿着直线 ${\omega}=vQ$ 显示解离态，其中斜率 $v$ 是核间距离的增加率，$Q$ 是入射和散射 X 射线光子之间的动量传递。我们推导了这种关系，并使用 FRXS 从 520 nm 泵浦后的分子碘实验 TRXS 中提取状态特定动力学。观察到的动力学包括 $^{1}{\Pi}_{u}$ 和 $^{1}{\Sigma}_{g}^{+}$ 激发态的一光子和二光子解离，以及 B ($^{3}{\Pi}_{0u}^{+}$) 态上的振动波包。
Time-resolved x-ray scattering (TRXS) measures internuclear separations in a molecule following laser-induced photoexcitation. The molecular dynamics induced by the excitation laser may lie on one or several bound or dissociative electronic states. TRXS from these states can be difficult to isolate because they generally overlap in the angle-resolved x-ray scattering pattern $I(x,y,{\tau})$, where ${\tau}$ is the pump-probe delay and $x,y$ are the physical pixel positions. Here we show how standard transform methods can isolate the dynamics from individual states. We form the temporal Fourier transform, $\tilde{I}(x,y,{\omega})$$=\int_{-\infty}^{\infty} d\tau e^{-i\omega\tau} I(x,y,\tau)$. This frequency-resolved x-ray scattering (FRXS) signal segregates the bound states according to their vibrational frequencies, ${\omega}_i$, and also displays dissociative states along straight lines ${\omega}=vQ$, where the slope $v$ is the rate of increase of the internuclear distance and $Q$ is the momentum transfer between the incident and scattered x-ray photon. We derive this relation and use FRXS to extract state-specific dynamics from experimental TRXS from molecular iodine following a 520 nm pump. Dynamics observed include one- and two-photon dissociation of the $^{1}{\Pi}_{u}$ and $^{1}{\Sigma}_{g}^{+}$ excited states, and vibrational wave packets on the B ($^{3}{\Pi}_{0u}^{+}$)state.