title: Ab Initio Anharmonic Analysis of Vibrational Spectra of Uracil Using the Numerical-Analytic Implementation of Operator Van Vleck Perturbation Theory.
abstract: The numerical-analytic implementation of the operator version of the canonical Van Vleck second-order vibrational perturbation theory (CVPT2) is employed for a purely ab initio prediction and interpretation of the infrared (IR) and Raman anharmonic spectra of a medium-size molecule of the diketo tautomer of uracil (2,4(1H,3H)-pyrimidinedione), which has high biological importance as one of the four RNA nucleobases. A nonempirical, semidiagonal quartic potential energy surface (PES) expressed in normal coordinates was evaluated at the MP2/cc-pVTZ level of theory. The quality of the PES was improved by replacing the harmonic frequencies with the "best" estimated CCSD(T)-based values taken from the literature. The theoretical method is enhanced by an accurate treatment of multiple Fermi and Darling-Dennison resonances with evaluation of the corresponding resonance constants W and K (CVPT2+WK method). A prediction of the anharmonic frequencies as well as IR and Raman intensities was used for a detailed interpretation of the experimental spectra of uracil. Very good agreement between predicted and observed vibrational frequencies has been achieved (RMSD ∼4.5 cm(-1)). The model employed gave a theoretically robust treatment of the multiple resonances in the 1680-1790 cm(-1) region. Our new analysis gives the most reliable reassignments of IR and Raman spectra of uracil available to date.
authors.affiliation: †Lomonosov Moscow State University, Leninskiye Gory, 119991, Moscow, Russian Federation.|‡Chemieinformationssysteme, Universität Ulm, Albert Einstein Allee 47, D-89069 Ulm, Germany.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Krasnoshchekov
authors.affiliation: †Lomonosov Moscow State University, Leninskiye Gory, 119991, Moscow, Russian Federation.|‡Chemieinformationssysteme, Universität Ulm, Albert Einstein Allee 47, D-89069 Ulm, Germany.
authors.forename: Natalja
authors.initials: N
authors.lastname: Vogt
authors.affiliation: †Lomonosov Moscow State University, Leninskiye Gory, 119991, Moscow, Russian Federation.
authors.forename: Nikolay F
authors.initials: NF
authors.lastname: Stepanov
mesh_terms: D008956:Models, Chemical; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D014498:Uracil / Q000737:chemistry*; D014732:Vibration
chemical_list: D014498:Uracil