In a recent study published in the Journal of the American Chemical Society, a research team led by Profs. JIANG Ling and LI Gang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. WANG Lai-Sheng from Brown University, discovered that neutral boron oxide clusters (BO₃, B₂O₄, B₃O₆) contain key structural units—BO, BO₃, and B₂O₅—which are essential building blocks of the two-dimensional vitreous network. The findings provide important insights into the microstructure and growth mechanisms of vitreous materials.

Boron oxide is a fundamental component in a wide range of materials, from everyday glass to advanced optics and high-energy propellants. Under ambient pressure, bulk B₂O₃ adopts a vitreous structure characterized by a two-dimensional network. However, the molecular-level mechanisms underlying the formation and growth of this network have remained unclear. Neutral boron oxide clusters offer ideal model systems for investigating these structural evolutions, but experimental studies have long been hindered by the difficulty of size selection, as neutral clusters lack charge and are challenging to isolate and characterize.

Using a platform they previously developed—a neutral-cluster infrared spectroscopy station based on the Dalian Coherent Light Source—the team obtained size-selected IR spectra of neutral BO₃, B₂O₄, and B₃O₆ clusters. This system enables high-sensitivity dedicated infrared (IR) spectral detection, structural characterization, and reactivity studies of mass-selected neutral clusters, combined with a tunable vacuum ultraviolet free-electron laser (VUV-FEL) at the Dalian Coherent Light Source.

Comparison between the experimental spectra and high-level quantum chemical calculations reveals that all three clusters adopt planar structures. Structural analysis shows that BO₃, B₂O₄, and B₃O₆ are composed of BO, BO₃, and B₂O₅ units, respectively—key structural units that constitute the vitreous two-dimensional network. Further chemical bonding analyses indicate that the structural stability of these clusters arises from the synergy between the terminal B≡O groups and B–O σ bonds.

This work not only provides crucial spectral signatures for the key structural units of bulk boron oxides but also serves as a robust model system. The findings pave the way for systematic, size-dependent studies of larger systems to understand the stepwise formation and growth mechanisms of two-dimensional boron oxide networks.