Inside out Approach to Rotator State in Hydrogen-Bonded System-Experimental and Theoretical Cross-Examination in n-Octanol.

Michał Pocheć,Aneta Jezierska,Katarzyna M Krupka,Kazimierz Orzechowski,Jarosław J Panek

doi:10.3390/ijms23042138

Michał Pocheć, Aneta Jezierska + Show 3 more

Open Access

https://doi.org/10.3390/ijms23042138

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Abstract

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from C to −15 C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from −30 C to −15 C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car–Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect’s influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated—the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Highlights

Premelting, first introduced as a concept by Faraday [1,2] in the late 19th century is a phenomenon broadly examined in contemporary science [3,4,5,6,7,8]
Premelting as a whole can start as a disruption in the chains of single molecules and ends with formation of a quasi-liquid phase on the surface
We have focused on time evolution methods: (i) classical molecular dynamics (MD); (ii) Car–Parrinello molecular dynamics (CPMD) [34]; (iii) path integral molecular dynamics (PIMD) [35,36]

Summary

Introduction

Premelting, first introduced as a concept by Faraday [1,2] in the late 19th century is a phenomenon broadly examined in contemporary science [3,4,5,6,7,8]. Dynamical process, it is very hard to investigate—the underlying molecular behavior, and other parameters are, by their very nature, gradually changing [9] It is uniform for solid-to-liquid phase transition and consists of the creation of a thin, liquidlike film on the surface of the solid. The second type of premelting behavior is rotator state (or phase) formation [14] It takes place in the broader temperature range at surface premelting, and it is more intricate. It is highly dependent on the type of the studied compound, the inter- and intramolecular interactions, or even the exact composition of molecules. The description needs to implement observations from all these mechanisms [13,16,17]

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