THE INFRARED-SPECTRA OF MATRIX-ISOLATED URACIL AND THYMINE - AN ASSIGNMENT BASED ON NEW THEORETICAL CALCULATIONS

The IR spectra of uracil and thymine predicted theoretically at the ab initio Hartree-Fock level with 6-31G** basis set are reported and compared with Ar matrix experimental spectra. The IR spectra computed at the SCF/6-31G** level reproduce the experimental spectra with an accuracy which allows a reliable vibrational assignment. A split valence basis set, augmented with polarization functions on all atoms, was found to be quite sufficient for a reliable prediction and assignment of the IR absorption bands in the spectra of medium-sized molecules.