Showing papers by "Maciej J. Nowak published in 1984"

Vibrational spectra of uracils: Experimental infrared matrix studies and ab initio quantum‐mechanical calculations

Abstract: New experimental studies of the infrared spectra of uracil, 1-methyluracil, 3-methyluracil, and 1,3-dimethyluracil all isolated in Ar matrices at 10 K are compared with calculated spectra. The calculations for uracil are ab initio quantum-mechanical calculations of frequencies and intensities reported by us recently, and the CNDO calculations by Harsanyi and Csaszar. Both simulated calculated spectra agree quite well with the experimental infrared spectrum of matrix isolated uracil. Additional calculations have been made for the methyl-substituted uracils by transferring the ab initio calculated force constants and intensity parameters from uracil. A comparison of these calculated infrared spectra for 1-methyl-, 3-methyl-, and 1,3-dimethyluracil with the experimental spectra indicates the quality of the agreement. The potential-energy distributions are given for all the fundamental modes of the deuterated uracil derivatives and for the methyluracil molecules for the three fundamental vibrations of these molecules in the carbonyl region (1600–1800 cm−1). This comparison indicates the effect of methyl and deuterium substitution on the relative contributions of C2O, C4O, and C5C6 stretching motions to each fundamental mode. This result explains the puzzling anomalies in the intensity patterns observed experimentally in this region of the spectra of isolated deutero- and methyl-substituted uracil molecules.