Ultrafast time-resolved x-ray scattering (TRXS) from a photoexcited molecular ensemble measures a distribution S(Q, τ) of the x-ray momentum transfer Q and pump-probe delay τ in which all modes of motion induced by the excitation overlap. Frequency-resolved x-ray scattering (FRXS) based on separates each oscillation and dissociation channel in the TRXS data, enabling measurements of vibrational frequencies and phases, and dissociation velocities and time shifts. Here we extend FRXS analysis to study early-time accelerations as well. We show how these appear as diffuse scattering patterns with characteristic phase evolution in FXRS and we develop a set of transformations that isolate individual channels to measure the early-time accelerated motion. This procedure is used to analyze diatomic iodine x-ray scattering data with multiple dissociations, and the ability of this technique to characterize early-time accelerations of one dissociation channel even in the presence of another dissociation is demonstrated.

来自光激发分子集合体的超快时间分辨X射线散射（TRXS）测量了X射线动量传递Q和泵浦探测延迟τ的分布S（Q，τ），其中由激发引起的所有运动模式重叠。频率分辨X射线散射（FRXS）基于分离TRXS数据中的每个振荡和解离通道，从而能够测量振动频率和相位以及解离速度和时移。在这里，我们扩展了FRXS分析以研究早期加速。我们展示了这些如何在FXRS中以具有特征性相位演化的弥散散射模式出现，并且我们开发出了一组隔离单个通道以测量早期加速运动的变换。该程序用于分析具有多个解离的双原子碘X射线散射数据，并且证明了该技术表征一个解离通道的早期加速度的能力，即使在存在另一个解离的情况下也是如此。