Analysis of the vibrational spectrum of 6-methyluracil by ab initio calculation

Abstract

The harmonic vibrational force field of 6-methyluracil has been computed at the ab initio Hartree-Fock level using a 4/2-21 basis set of Gaussian orbitals. A set of scaling factors, optimized for 1-methyluracil, was transferred unchanged and used to scale the force field computed for this closely related molecule. Dipole-moment derivatives were also computed. The spectrum of fundamental frequencies and absorption intensities was computed from the scaled force field and compared with previous experimental assignments of the gas-phase and matrix spectra. Mean deviations between computed frequencies and the matrix data were 8.2 cm −1 for the inplane modes and 14.4 cm −1 for the out-of-plane ones. One transition, the v 21 CO wagging motion, is believed to have been previously misassigned.