Dimers of tetracene molecules are formed inside helium nanodroplets and identified through covariance analysis of the emission directions of kinetic tetracene cations stemming from femtosecond laser-induced Coulomb explosion. Next, the dimers are aligned in either one or three dimensions under field-free conditions by a nonresonant, moderately intense laser pulse. The experimental angular covariance maps of the tetracene ions are compared to calculated covariance maps for seven different dimer conformations and found to be consistent with four of these. Additional measurements of the alignment-dependent strong-field ionization yield of the dimer narrow the possible conformations down to either a slipped-parallel or parallel-slightly rotated structure. According to our quantum chemistry calculations, these are the two most stable gas-phase conformations of the dimer and one of them is favorable for singlet fission.

中文翻译：

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使用飞秒强场电离确定氦纳米液滴中并四苯二聚体的结构。

并四苯分子的二聚体在氦纳米液滴内形成，并通过对飞秒激光诱导库仑爆炸产生的动态并四苯阳离子的发射方向进行协方差分析来识别。接下来，二聚体在无场条件下通过非共振、中等强度的激光脉冲在一维或三维上排列。将并四苯离子的实验角协方差图与七种不同二聚体构象的计算协方差图进行比较，发现与其中四种一致。对二聚体的排列依赖性强场电离产率的额外测量将可能的构象缩小到滑动平行或平行轻微旋转结构。根据我们的量子化学计算，这是二聚体的两种最稳定的气相构象，其中之一有利于单线态裂变。