The hydration effect on the uracil frequencies: an experimental and quantum chemical study

This work describes the performance of different quantum chemical theoretical methods in calculating the vibrational frequencies of uracil and some derivatives, and the effect of hydration on the uracil frequencies. The Raman spectra of polycristalline uracil with different water contents are discussed. To correct the deficiency of the theoretical quantum chemical methods, several procedures are described in detail. Two of them are new. For these new procedures, scaling factors and scaling equations were determined at different levels. With them, a significant reduction in the error of the predicted frequencies was obtained over the one-factor scaling standard procedure. A comparison of the cost/effective method and procedure of scaling was carried out on uracil molecule. Scale factors transferred from uracil to related molecules provided an a priori prediction of fundamental frequencies and intensities, permitting several corrections to be proposed for earlier assignments. (C) 2002 Elsevier Science B.V. All rights reserved.