An ab initio post-Hartree-Fock study of vibrational infrared spectra of 5-azacytosine and cytosine

Post-Hartree-Fock ab initio studies were performed to predict the infrared (IR) vibrational spectra of the two most stable tautomers of 5-azacytosine and cytosine. All geometries were optimized without symmetry restrictions b y the gradient procedure at the MP2 level of theory using the standard 6-31 G(d,p) basis set. IR spectra have been calculated at the MP2/6-31G(d,p) app roximation. We found similar patterns in the sequence of the modes of the h armonic frequencies for both cytosine and 5-azacytosine in the 3400-900 cm( -1) region and distinctive differences in the high-frequency region. (C) 20 01 John Wiley & Sons, Inc.