The constant vibration/rotation and hydrogen-bond (HB) rearrangement of water molecules create various complex yet dynamic HB networks, rendering the structure of liquid water difficult to characterize. Inasmuch as the nature of the intermolecular forces between water molecules in water clusters bears resemblance to that in the bulk, spectroscopic studies of water clusters not only reveals the basic building blocks of the HB network but also provides central benchmarks for developing accurate potential functions and universal models of water.
In a study published inNature Communications, a research team led by Prof. JIANG Ling and Prof. LI Gang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. LI Jun from Tsinghua University has unveiled experimentally the structure motifs of water undecamer cluster (H2O)11.
Experimental IR spectrum and identified structures of water undecamer cluster (H2O)11 (Image by WANG Tiantong)
Profs. JIANG Ling and LI Gang developed a method of infrared spectroscopy of neutral clusters based on a tunable vacuum ultraviolet free electron laser (VUV-FEL). They applied this method to neutral (H2O)11, and recorded the IR spectrum with diverse bands.
By combining IR spectrum with high-precision quantum chemical computations from LI Jun's group, three lowest-energy configurations denoted as 515, 43'4, and 55'1 structural motifs were determined. These structures correspond to the "5+1+5", "4+3+4", and "5+5+1" assembling of water cluster pairs, respectively, with the 515 configuration being dominant.
Furthermore, the cluster growth mechanisms from water decamer clusters were revealed through thermodynamic analysis. The research offers crucial insights into the evolution of water's HB network and paves the way for size-dependent studies for exploring the stepwise mechanisms of solvation processes such as salt dissolution and acid dissociation.