Abstract
Infrared (IR) spectroscopy is commonly used in chemical laboratories to study the geometrical structure of molecules and molecular complexes. The analysis of experimental IR spectra can nowadays be reliably supported by the results of quantum-chemical computations as vibrational frequencies and corresponding vibrational transition intensities are routinely calculated using harmonic approximation by virtually all quantum chemistry packages. In the present study we combine the methodology of computing vibrational spectra using high-level electron correlation treatments with an analytical potential-based approach to take into account spatial confinement effects. Using this approach, we perform a pioneering analysis of the impact of the spatial confinement caused by a cylindrical harmonic oscillator potential on the harmonic vibrational transition intensities and frequencies of two hydrogen-bonded complexes: HCN…HCN and HCN…HNC. The emphasis is put on the largest-intensity bands, which correspond to the stretching vibrations. The obtained results demonstrate that embedding the molecular complexes in an external confining potential causes significant changes of transition intensities and vibrational frequencies.
Highlights
In the present study we demonstrated that the spatial confinement simulated by a cylindrical harmonic oscillator potential significantly affects vibrational spectra of hydrogen-bonded molecular complexes
We highlight that in order to predict IR spectra of confined species with high accuracy it is mandatory to account for anharmonicity effects
Summary
Studies of molecular structure using infrared spectroscopy have become a fairly routine task and nowadays IR spectrometers are part of virtually all chemical laboratories. High-level electron-correlation methods can be used for band assignments in vibrational spectra of small- and medium-sized molecules and molecular complexes. They can be used to map the changes in infrared vibrational spectroscopic signatures to structural changes. The present study contributes to these theoretical efforts and its goal is to apply the methodology to compute the harmonic infrared vibrational spectra using high-level electron correlation treatments to spatially confined hydrogen-bonded molecular complexes
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