National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
J Chem Phys. 2013 Jul 14;139(2):024304. doi: 10.1063/1.4812787.
Experiments in the gas phase usually involve averaging observables over a random molecular axis alignment distribution. This deleterious averaging limits insights gained by probes of molecular dynamics, but can be overcome by prealigning molecular axes using laser-alignment methods. However, the transformation from the laboratory frame to the molecular frame of reference requires quantitative knowledge of the axis alignment distribution. The latter is often hard to obtain directly from experimental data, particularly for polyatomic molecules. Here we describe a general maximum-likelihood classification procedure for non-adiabatic numerical alignment simulations with free parameters that employs experimental data from an alignment-dependent probe. This method delivers (i) the most probable molecular frame angular dependence of the probe, and (ii) the most likely laboratory frame axis alignment distribution of the sample, each with a confidence interval. This procedure was recently used for studies of angle- and channel-resolved strong field ionization of 1,3-butadiene in the molecular frame [Mikosch et al., Phys. Rev. Lett. 110, 023004 (2013)], used here as an illustrative example.
气相实验通常涉及对随机分子轴取向分布进行可观测量的平均化。这种有害的平均化限制了通过分子动力学探针获得的见解，但可以通过激光对准方法预先对准分子轴来克服。然而，从实验室框架到分子参考框架的转换需要定量了解轴取向分布。后者通常很难直接从实验数据中获得，特别是对于多原子分子。在这里，我们描述了一种通用的最大似然分类程序，用于具有自由参数的非绝热数值对准模拟，该程序采用来自对准相关探针的实验数据。该方法提供了（i）探针的最可能分子框架角依赖性，以及（ii）样品的最可能实验室框架轴对准分布，两者均带有置信区间。该程序最近用于在分子框架中研究 1,3-丁二烯的角度和通道分辨强场电离[Mikosch 等人，Phys. Rev. Lett. 110, 023004（2013）]，这里将其用作说明性示例。
