Capturing the hydrogen radical is of central importance in various systems ranging from catalysis to biology to astronomy, but it has been proven to be challenging experimentally because of its high reactivity and short lifetime. Here, neutral MO 3 H 4 (M = Sc, Y, La) complexes were characterized by size-specific infrared-vacuum ultraviolet spectroscopy. All these products were determined to be the hydrogen radical adducts in the form of H•M(OH) 3 . The results indicate that the addition of the hydrogen radical to the M(OH) 3 complex is both thermodynamically exothermic and kinetically facile in the gas phase. Moreover, the soft collisions in the cluster growth channel with the helium expansion were found to be demanded for the formation of H•M(OH) 3 . This work highlights the pivotal roles played by the soft collisions in the formation of hydrogen radical adducts and also opens new avenues toward the design and chemical control of compounds.
Structural characterization of neutral water clusters is crucial to understanding the structures and properties of water, but it has been proven to be a challenging experimental target due to the difficulty in size selection. Here, we report the size-specific infrared spectra of confinement-free neutral water nonamer (H2O)9 based on threshold photoionization, using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals in the 3200–3350 cm−1 region are observed, providing unique spectral signatures for the formation of an unprecedented (H2O)9 structure evolved by adding a ninth water molecule onto a hydrogen bond-unbroken edge of the (H2O)8 octamer with D2 d symmetry. This nonamer structure coexists with the five previously identified structures that can be viewed as derived by inserting a ninth water molecule into a hydrogen bond-broken edge of the D2 d/ S4 octamer. These findings provide key microscopic information for systematic understanding of the formation and growth mechanism of dynamical hydrogen-bonding networks that are responsible for the structure and properties of condensed-phase water.
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