Towards complete assignment of the infrared spectrum of the protonated water cluster H<sup>+</sup>(H<sub>2</sub>O)<sub>21</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34686665.
- Also identified by DOI 10.1038/s41467-021-26284-x and PMC identifier 8536673.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H<sup>+</sup>(H<sub>2</sub>O)<sub>n</sub> extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H<sup>+</sup>(H<sub>2</sub>O)<sub>21</sub> cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster.