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Quantum fluid droplets made of helium-3 (3He) or helium-4 (4He) isotopes have long been considered as ideal cryogenic nanolabs, enabling unique ultracold chemistry and spectroscopy applications. The droplets were believed to provide a homogeneous environment in which dopant atoms and molecules could move and react almost as in free space but at temperatures close to absolute zero. Here, we report ultrafast x-ray diffraction experiments on xenon-doped 3He and 4He nanodroplets, demonstrating that the unavoidable rotational excitation of isolated droplets leads to highly anisotropic and inhomogeneous interactions between the host matrix and enclosed dopants. Superfluid 4He droplets are laced with quantum vortices that trap the embedded particles, leading to the formation of filament-shaped clusters. In comparison, dopants in 3He droplets gather in diffuse, ring-shaped structures along the equator. The shapes of droplets carrying filaments or rings are direct evidence that rotational excitation is the root cause for the inhomogeneous dopant distributions.

Previous single-pulse extreme ultraviolet and x-ray coherent diffraction studies revealed that superfluid He4 droplets obtained in a free jet expansion acquire sizable angular momentum, resulting in significant centrifugal distortion. Similar experiments with normal fluid He3 droplets may help elucidate the origin of the large degree of rotational excitation and highlight similarities and differences of dynamics in normal and superfluid droplets. Here, we present a comparison of the shapes of isolated He3 and He4 droplets following expansion of the corresponding fluids in vacuum at temperatures as low as ∼2 K. Large He3 and He4 droplets with average radii of ∼160 and ∼350 nm, respectively, were produced. We find that the majority of the shapes of He3 droplets in the beam correspond to rotating oblate spheroids, in agreement with previous observations for He4 droplets. The aspect ratio of the droplets is related to the degree of their rotational excitation, which is discussed in terms of reduced angular momenta (Λ) and reduced angular velocities (ω), the average values of which are found to be similar in both isotopes. This similarity suggests that comparable mechanisms induce rotation regardless of the isotope. We hypothesize that the observed distribution of droplet sizes and angular momenta originates from processes in the dense region close to the nozzle, where a significant velocity spread and frequent collisions between droplets induces excessive rotation followed by droplet fission.

The conformational space of cis-1,2-cyclohexanediol, a model molecule for cyclic vicinal diols, was investigated using rotational spectroscopy and density functional theory calculations. Four low energy conformers within an energy window of 5 kJ mol−1 were identified computationally. A rotational spectrum of jet-cooled cis-1,2-cyclohexanediol was recorded with a chirped pulse Fourier transform microwave spectrometer. Two sets of rotational transitions were observed and could be assigned to conformers of cis-1,2-cyclohexanediol. The non-observation of other low energy conformers was explained by conformational conversion barrier height calculations and results from experimental spectra recorded with different carrier gases. Eight isotopologues, including those with 13C and 18O, of the lowest energy conformer were observed, allowing the determination of the semi-experimental equilibrium structure, reSE. Interestingly, the structural analysis revealed that the C–O bond length of the intramolecular hydrogen-bond donor is shorter than that of the acceptor. This appears to be a general characteristic of vicinal diols and can be used as a novel hydrogen-bond marker in such compounds. [ABSTRACT FROM AUTHOR]

The conformational landscapes of four 1‐O‐methylated monosaccharides—methyl α‐glucose, methyl β‐glucose, methyl α‐galactose, and methyl β‐galactose—were characterized using jet‐cooled broadband rotational spectroscopy, supported by density functional theory calculations. A newly designed, simple pulsed nozzle assembly was used to introduce the sugar samples into a jet expansion without thermal degradation, eliminating the need for a complex and expensive laser ablation system. Ten conformers were experimentally identified by assigning their rotational spectra, and the intricate methyl internal rotation splittings were analysed. Notably, methylation alters the directionality of intramolecular hydrogen bonding of α‐galactose highlighting its impact on structural preference. Natural bond orbital, intrinsic bond strength, and non‐covalent interaction analyses were conducted to explore the interplay between hydrogen bonding and hyperconjugation. A set of σ to σ* neutral hyperconjugative interactions was found to override a strong hydrogen bond, driving a preference for the gauche conformers. [ABSTRACT FROM AUTHOR]

This study delves into driving forces behind the formation of a hetero ternary cluster consisting of volatile organic compounds from industrial or combustion sources, specifically cyclopentene, alongside greenhouse gases like carbon dioxide, and water vapor. While substantial progress has been made in understanding binary complexes, the structural intricacies of hetero ternary clusters remain largely uncharted. Our research characterized the cyclopentene−CO2−H2O hetero ternary cluster utilizing Fourier transform microwave spectroscopy. The observed isomer in the pulsed jet has CO2 and H2O aligning above the cyclopentene ring, with water undergoing an internal rotation approximately about its C2 symmetry axis. Theoretical analyses support these observations, identifying an O−H⋅⋅⋅π hydrogen bond and a secondary C⋅⋅⋅O tetrel bond within this cluster. This study marks a critical step towards comprehending the molecular dynamics and interactions of VOCs, greenhouse gases, and water in the atmosphere, paving the way for further investigations into their roles in climate dynamics and air quality. [ABSTRACT FROM AUTHOR]

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