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Stability and Anharmonic N-H Stretching Frequencies of 1-Methylthymine Dimers: Hydrogen Bonding versus π-Stacking
Milena Petković1, Miroslav Ristić1, Mihajlo Etinski1
1Faculty of Physical Chemistry, University of Belgrade Studentski trg 12-16, 11 158 Belgrade, Serbia.
Abstract:
Stability of three hydrogen-bonded and six stacked 1-methylthymine (1 mT) dimers was studied with the DFT-D3 method at various temperatures. It was demonstrated that the stacked dimers are slightly less stable than the hydrogen-bonded counterparts. Existence of T-shaped dimers is addressed. Anharmonic couplings that involve N-H stretching modes of the nine species are studied. Surprisingly, we find that N-H stretching modes of the two 1 mT molecules are significantly coupled in four stacked dimers. The presented results shed light on existence of strong mode couplings between the two N-H stretching modes in stacked aromatic species. Our calculations support the proposal ( J. Phys. Chem. A 2011 , 115 , 9429 - 9439 ) that presence of several dimers is responsible for appearance of wide and structured bands in 1 mT homodimers' jet-cooled spectra above 2900 cm(-1).
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