GROUND-STATE VIBRATIONS OF GUANIDINIUM AND METHYLGUANIDINIUM IONS - AN AB-INITIO STUDY

The results of ab initio SCFMO calculations using 6-31G* basis set for guanidinium - d0,d6 and methylguanidinium - d0,d5 ions are presented. The optimized geometries from these calculations have been compared with experimental bond distances and bond angles obtained from crystal structures. The vibrational spectra (frequencies and intensities) for the compounds and their deuterated isotopomers have been calculated using the same basis set. The predicted spectra have been compared with the experimental IR and Raman spectra of the molecules and their isotopomers in solid state as well as in solution. The calculated potential energy distribution provides a basis for assigning the experimental spectra. The isotopic frequency shifts for H-2 substituted guanidinium ion and methylguanidinium ion are also found to be in close agreement with the experimental isotopic frequency shift. The calculated IR intensity pattern also shows good agreement with the experimental spectrum.