N-18 - A COMPUTATIONAL INVESTIGATION

Ab initio quantum mechanics methods have been applied to study the cag e-like polynitrogen cluster N-18 The previously reported cage-like str ucture of the N-18 molecule with symmetry C-2v has been optimized at t he RHF/4-31G, RHF/6-31G*, DFT(B3LYP, B3P86, BHLYP)/6-31G* and MP2(ful l)/6-31G levels of theory. The harmonic vibration frequencies and the ir infrared (IR) and Raman intensities have also been reported at RHF/ 4-31G, RHF/6-31G*, as well as the B3P86/6-31G* level. The results sho w that the investigated cage-like structure is stable on the potential energy hypersurface, lying above separated nitrogen molecules by abou t 50 kcal mol(-1) of nitrogen atoms, with a stability comparable with the dodecahedral N-20 molecule. The resultant structure also suggests the aromaticity of conjugated pentagons which stabilizes the cage-like polynitrogen clusters. (C) 1998 Elsevier Science B.V.