Interpreting the vibrational spectra of uracil molecules and their deuterated isotopomers using a scaled quantum-chemical quadratic force field

The quadratic force field of the uracil molecule is obtained by MP2(full) calculations using the cc-pVTZ and cc-pVQZ basis sets. Under the assumption that the most stable diketone form of the uracil molecule has a flat configuration with Cs symmetry, the available vibrational gas-phase spectra of uracil and the matrix isolation spectra of its seven N-, C-, and mixed N,C-deuterated derivatives are analyzed jointly for the first time by using Pulay’s force field scaling. Band assignments suggested earlier are corrected. It is shown that sets of 14 scaling factors allow us to reproduce the adjusted interpretation of the spectra and to obtain the most reliable quadratic force constant matrix for uracil among those available, based on joint consideration of the experimental and quantum-chemical calculation results.