气相双原子分子时间分辨X射线散射中离解运动的表征
Characterizing dissociative motion in time-resolved x-ray scattering from gas-phase diatomic molecules
摘要：
时间分辨X射线散射（TRXS）测量激光诱导光激发后分子中的核间分离。由激发激光诱导的分子动力学可以取决于一个或多个束缚或解离电子态。来自这些状态的TRXS可能难以隔离，因为它们通常在角度分辨X射线散射图案$I(x,y,τ)$中重叠，其中$τ$是泵浦-探测延迟，而$x,y$是物理像素位置。在这里，我们将展示如何标准的转换方法可以隔离的动态从个别国家。我们形成时间傅里叶变换，$\tilde{I}(x,y,ω)$ $=\int_{-\infty}^{\infty} dτe^{-iωτ} I(x,y,τ)$。该频率分辨X射线散射（FRXS）信号根据束缚态的振动频率$ω_i$分离束缚态，并且还沿着直线$ω=vQ$显示解离态，其中斜率$v$是核间距的增加率，$Q$是入射和散射的X射线光子之间的动量转移。我们推导出这种关系，并使用FRXS提取状态特定的动力学从实验TRXS分子碘后，520 nm的泵。观察到的动力学包括$^{1}Π_{u}$和$^{1}Σ_{g}^{+}$激发态的单光子和双光子解离，以及B（$^{3}Π_{0u}^{+}$）态的振动波包。
英文摘要：
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 $I(x,y,τ)$, where $τ$ 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,ω)$$=\int_{-\infty}^{\infty} dτe^{-iωτ} I(x,y,τ)$. This frequency-resolved x-ray scattering (FRXS) signal segregates the bound states according to their vibrational frequencies, $ω_i$, and also displays dissociative states along straight lines $ω=vQ$, 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 $^{1}Π_{u}$ and $^{1}Σ_{g}^{+}$ excited states, and vibrational wave packets on the B ($^{3}Π_{0u}^{+}$)state.
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