Imaging collective quantum fluctuations of the structure of a complex molecule.

Because of the Heisenberg uncertainty principle, the structure of a molecule fluctuates about its mean geometry, even in the ground state. Observing this fundamental quantum effect experimentally—particularly, revealing the collective nature of the structural quantum fluctuations—remains an unmet challenge for complex molecules. In this work, we achieved this for an 11-atom molecule by inducing its Coulomb explosion with an x-ray free-electron laser. We show that the structural fluctuations manifest themselves in correlated variations of ion momenta obtained through coincident detection of the atomic fragments from individual molecules. Our analysis scheme allows extracting these variations, despite our measurements covering only a fraction of the full 33-dimensional momentum space, thereby establishing a general approach for extracting information on high-dimensional structural dynamics using Coulomb explosion. Editor's summary: Quantum ground-state fluctuations are crucial phenomena in nature, affecting various processes, including quantum phase transitions and chemical reactions. Earlier studies on the topic only showed single fluctuating bond angles or bond distances, such as those in triatomic molecules. Richard et al. used the distinctive capabilities of x-ray–induced Coulomb explosion imaging to obtain accurate single-molecule data, which enabled the direct observation of collective fluctuations across all atoms in the complex polyatomic molecule 2-iodopyridine (C5H4NI). The presented method advances the ability to address various time-resolved chemistry experiments that present a formidable challenge for other time-resolved imaging techniques that typically rely on averaging measurements over many molecules. —Yury Suleymanov [ABSTRACT FROM AUTHOR]