Exploring the next step in micro-solvation of CO in water: Infrared spectra and structural calculations of (H2O)4- CO and (D2O)4- CO

TL;DR

This study combines high-resolution IR spectroscopy and ab initio calculations to analyze the structure of CO micro-solvation in water tetramers, revealing detailed geometric arrangements and hydrogen bonding patterns.

Contribution

It provides the first detailed structural analysis of (H2O)4-CO and (D2O)4-CO complexes, extending understanding of CO solvation at the molecular level.

Findings

(H2O)4-CO spectrum is broadened by predissociation, D2O spectrum is sharp.

The water tetramer forms a cyclic ring similar to isolated water tetramer.

The CO is positioned above the ring with a partial hydrogen bond.

Abstract

We extend studies of micro-solvation of carbon monoxide by a combination of high-resolution IR spectroscopy and ab initio calculations. Spectra of the (H2O)4-CO and (D2O)4-CO pentamers are observed in the C-O stretch fundamental region (~2150 cm-1). The H2O containing spectrum is broadened by predissociation, but that of D2O is sharp, enabling detailed analysis which gives a precise band origin and rotational parameters. Ab initio calculations are employed to confirm the assignment to (water)4-CO and to determine the structure, in which the geometry of the (water)4 fragment is a cyclic ring very similar to the isolated water tetramer. The CO fragment is located "above" the ring plane, with a partial hydrogen bond between the C atom and one of the "free" protons (deuterons) of the water tetramer. Together with previous results on D2O-CO, (D2O)2-CO, and (D2O)3-CO, this represents a probe of the four initial steps in the solvation of carbon monoxide at high resolution.