Физика Низких Температур: Том 47, Выпуск 4 (Апрель 2021), c. 355-364 ( к оглавлению , назад )
Coronene-uracil complexes embedded in argon matrices: FTIR spectroscopy and quantum-mechanical calculations
S. G. Stepanian, A. Yu. Ivanov, and V. A. Karachevtsev
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine Kharkiv 61103, Ukraine
Department of Chemistry and Biochemistry, University of ArizonaTucson, Arizona 85721, USA
Received October 31, 2020, published online February 26, 2021
We employ low-temperature matrix-isolation FTIR spectroscopy and quantum chemical calculations to study the interaction between nucleobase uracil and coronene which models the graphene surface. To observe the dimer FTIR spectrum, we use a quartz microbalance that allows us to produce matrix samples with precisely determined concentrations of coronene and uracil (with the concentration ratio of 2.5:1:1000 for coronene:uracil:argon).The interaction between coronene and uracil results in spectral shifts of uracil spectral bands. These shifts do not exceed 10 cm–1. The maximum shifts are observed for the C=O stretching and NH out-of-plane vibrations of uracil. The structures and interaction energies of stacked and H-bonded coronene-uracil complexes are calculated at the DFT/B3LYP(GD3BJ)/aug-cc-pVDZ and MP2/aug-cc-pVDZ levels of theory. In total, 19 stable stacked and two H-bonded coronene-uracil dimer structures are found in the calculations. The interaction energy obtained for the most stable stacked dimer is – 12.1 and – 14.3 kcal/mol at the DFT and MP2 levels, respectively. The interaction energies of the H-bonded dimers do not exceed – 3 kcal/mol. The IR spectra of the studied monomeric molecules and of all the dimers are calculated at the DFT/B3LYP(GD3BJ)/aug-cc-pVDZ level of theory. The spectral shifts of the most stable stacked coronene-uracil dimer obtained in the calculations are in good agreement with the experimental results.
Key words: low-temperature matrix isolation, FTIR spectroscopy, coronene, uracil, stacking.