The coupling of localised, vibrational modes - Probing OH-bands of organic molecules via a two dimensional Numerov approach

Manuel J Schuler; Raphael Henn; Christian G Kirchler; Inge Schlapp-Hackl; Christian W Huck; Thomas S Hofer

doi:10.1016/j.saa.2019.117377

The coupling of localised, vibrational modes - Probing OH-bands of organic molecules via a two dimensional Numerov approach

Spectrochim Acta A Mol Biomol Spectrosc. 2020 Jan 5:224:117377. doi: 10.1016/j.saa.2019.117377. Epub 2019 Jul 23.

Authors

Manuel J Schuler¹, Raphael Henn², Christian G Kirchler², Inge Schlapp-Hackl¹, Christian W Huck², Thomas S Hofer³

Affiliations

¹ Institute of General, Inorganic and Theoretical Chemistry, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82, Innsbruck A-6020, Austria.
² Institute of Analytical Chemistry and Radiochemistry, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82, Innsbruck A-6020, Austria.
³ Institute of General, Inorganic and Theoretical Chemistry, Center for Chemistry and Biomedicine, University of Innsbruck, Innrain 80-82, Innsbruck A-6020, Austria. Electronic address: T.Hofer@uibk.ac.at.

PMID: 31400743
DOI: 10.1016/j.saa.2019.117377

Abstract

In this article the extension of the grid-based Numerov approach to probe two coupled, localised vibrational modes is assessed. The theoretically obtained wave numbers are compared to experimental results for five increasingly complex organic molecules carrying two OH groups measured in gas-phase as well as carbon tetrachloride. By using an appropriate spacing of the associated potential energy grid a deviation of the predicted wave numbers with experiment of ≤1% is achieved for both the fundamental and the first overtone bands. In particular the calculated wave numbers of aliphatic species in vacuum underline the versatility of this approach. In addition, it is demonstrated that bicubic interpolation is a viable strategy to greatly reduce the required data points and thus, the computational effort. Comparison of predicted wave numbers obtained for different conformers with experimental data enables the identification of the most relevant conformer present in solution. Since especially the accurate calculation of overtone vibrations is known to be challenging in case of strongly anharmonic potentials such as OH bonds, the presented approach provides a particularly efficient route to study the properties of the associated overtone contribution under the influence of inter-mode coupling. This is due to the fact that the Numerov approach requires no assumption about form and composition of the vibrational wave functions. In addition, the presented method also provides one of the simplest routes to access combined excitations of the considered vibrational modes.

Keywords: Grid-based; Infrared; Method development; Near infrared; Numerov method; Quantumchemical calculations; Theoretical chemistry; Vibrational spectroscopy.