# Understanding the Influence of a Water Molecule in the Structure of a Dimer

## TL;DR

This study explores how water interacts with organic dimers, revealing that water tends to add to rather than insert into hydrogen bond networks.

## Contribution

The work provides new insights into how different donor types influence hydration patterns and spectroscopic signatures in organic dimers.

## Key findings

- All systems except PET2 form similar monohydrated structures where water adds to the hydrogen bond network.
- OH···S and OH···N interactions show similar spectroscopic shifts despite differing electronic characteristics.
- Computational analysis confirms the most stable isomers observed experimentally.

## Abstract

Understanding how water influences molecular aggregation
is essential
for interpreting noncovalent interactions in biological and chemical
systems. In this study, we investigate the solvation of organic dimers
formed by 2-phenylethanol (PEAL), 2-phenethylamine (PEA), and 2-phenethylthiol
(PET) through a combination of two-color REMPI and IR-UV double resonance
spectroscopy, supported by quantum chemical calculations. Despite
the structural and electronic differences among the three molecules,
all systemsexcept PET2form similar monohydrated
structures, where water adds to the preexisting hydrogen bond network
rather than inserts into it. The observed behavior seems to follow
qualitative energetic trends, with the most stable structures favored
under the experimental conditions; structural accessibility could
also influence the formation of certain isomers. Spectroscopic shifts
in OH, NH, and SH stretching regions reveal correlations between OH···S
and OH···N interactions, despite their differing electronic
characteristics, while the OH···O interaction needs
to be stronger to induce comparable shifts. Computational analysis
confirms that the experimentally observed structures correspond to
the most stable isomers, although alternative cyclic structures were
also identified with slightly higher energies. By systematically comparing
dimers formed by OH-, NH-, and SH-containing molecules, this work
extends previous studies on water insertion versus addition and provides
new insights into how donor type influences hydration patterns and
spectroscopic signatures.