Normal coordinate treatment of 1-methyluracil in the crystal state: Use of the ultraviolet resonance Raman intensities to improve the vibrational force field

Abstract

Normal modes of 1-methyluracil in the crystal state have been determined using a general valence force field. In-plane force constants have been deduced from relations between ultraviolet resonance Raman intensities (UVRR), variations in bond orders from the ground to the electronic excited states and frequencies. Positions for molecules in the orthorhombic system (space group Ibam) were deduced from lattice energy calculations. A very good agreement in the normal modes assignments is obtained with previous works, leading to confidence with the use of UVRR intensities to deduce adequate force-fields.