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

摘要

In this study, the geometrical structure and vibrational spectrum are studied for the N,N'-dimethylurea molecule [CO(NHCH_3)_2] (DMU) in the gas phase as well as in its Cc crystal phase. The vibrational spectrum of DMU was interpreted by measuring the solid state state infrared spectra of normal, partially and totally deuterated DMU at room temperature and at -196 ℃, and the Raman spectra of the solid state at room temperature and at -120 ℃, and of DMU-water the DMU-chloroform solutions. Using calculations at the RHF/6-31++G~(**) level, the equilibrium geometry and harmonic force field for both the gas phase and the crystal phase are determined. The crystal phase is modeled using a 15 molecule cluster surrounded by 6048 point charges.