Solids modeled by ab initio crystal field methods. 21. Study of the structure and vibrational spectrum of N,N '-dimethylurea in the gas phase and in its Cc crystal phase

In this study, the geometrical structure and vibrational spectrum are studi ed for the N,N'-dimethylurea molecule [CO(NHCH3)(2)] (DMU) in the gas phase as well as in its Cc crystal phase. The vibrational spectrum of DMU was in terpreted by measuring the solid state state infrared spectra of normal, pa rtially and totally deuterated DMU at room temperature and at -196 degrees C, and the Raman spectra of the solid state at room temperature and at -120 degrees C, and of DMU-water and DMU-chloroform solutions. Using calculatio ns at the RHF/6-31++G** level, the equilibrium geometry and harmonic force field for bath the gas phase and the crystal phase are determined. The crys tal phase is modeled using a 15 molecule cluster surrounded by 6048 point c harges.