ABINITIO INVESTIGATION OF THE STRUCTURES AND STABILITIES OF CH2N2, CHFN2, AND CF2N2 ISOMERS - IMPORTANT CONSEQUENCES OF MP2 OPTIMIZATIONS

Ab initio calculations of the potential energy surfaces of CH2N2, CHFN2, and CF2N2 at MP4SDTQ/6-31G*//MP2(full)/6-31G* reveal several surprising features. While diazomethane is more stable than diazirine, only the three-membered ring forms of the fluorine-substituted isomers are known experimentally. We find fluorodiazomethane and difluorodiazomethane not to be viable species: They have no barriers toward exothermic dissociation into N2 and CHF or CF2, respectively. In contrast, the three-membered ring isomers, fluorodiazirine and difluorodiazirine, have high barriers toward dissociation despite being high in energy. Diazomethane bends easily; a nonplanar C(s) minimum is found at MP2(full)/6-31G* but C2v symmetry is preferred at QCISD/6-31G*.