Accurate Calculations of OH-Stretching Intensities with a Reduced-Dimensional Local Mode Model Including Eckart Axis Embedding

Emil Vogt; Pablo Bertran Valls; Henrik G Kjaergaard

doi:10.1021/acs.jpca.9b10682

Accurate Calculations of OH-Stretching Intensities with a Reduced-Dimensional Local Mode Model Including Eckart Axis Embedding

J Phys Chem A. 2020 Feb 6;124(5):932-942. doi: 10.1021/acs.jpca.9b10682. Epub 2020 Jan 24.

Authors

Emil Vogt¹, Pablo Bertran Valls¹, Henrik G Kjaergaard¹

Affiliation

¹ Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø Copenhagen , Denmark.

PMID: 31913643
DOI: 10.1021/acs.jpca.9b10682

Abstract

Absolute OH- and OD-stretching transition intensities have been calculated for a series of alcohols (methanol, ethanol, 2-propanol, 1-propanol, and tert-butanol) with one-dimensional (1D) and three-dimensional (3D) local mode models. We compare the calculated intensities for the Δv_OH = 1-5 and Δv_OD = 1-3 transitions with experimental values. Potential energy and dipole moment surfaces are calculated at the CCSD(T)-F12a/VDZ-F12 level of theory. The 1D local mode model includes only the OH(D)-stretching mode, whereas the 3D local mode model also includes the CO-stretching and COH(D)-bending modes. We analyze the effect on vibrational intensities of using either a molecule-fixed Eckart frame or a space-fixed Cartesian frame. We find that both Eckart embedding and inclusion of the CO-stretching and COH(D)-bending modes in the local mode model are important for the OH/OD-stretching fundamental transition intensities, but have a minor effect on overtone intensities. The 3D reduced-dimensional local model, when combined with coupled cluster surfaces, accurately predicts OH/OD-stretching transition intensities and wavenumbers, for all alcohols included in this work.