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Assigning the NH Stretches of the Guanine Tautomers Using Adiabatic Separation:  CCSD(T) Benchmark Calculations

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journal contribution
posted on 06.03.2008, 00:00 by Dana Nachtigallová, Pavel Hobza, Vladimír Špirko
Using an adiabatic separation of the NH stretching vibration from the remaining vibrational molecular motions, the NH fundamental frequencies and absolute intensities of several keto/enol and 7/9NH tautomers of guanine are evaluated ab initio within the framework of a one-dimensional “semirigid” stretching Hamiltonian. The frequencies (calculated by means of the standard MP2, CCSD(T) and DFT procedures) are in a close one-to-one harmony with their experimental counterparts, thus evidencing the adequacy of the used separation for reliable assigning of the NH stretches in the vibrational spectra of very large molecular systems.