Theoretical Investigation on Atmospheric Chemistry of Nitryl Cyanide: A Novel Fluorine-Free Dielectric Gas

In view of the significant greenhouse effect of sulfurhexafluorideand the potential biotoxic hazard of perfluorinated substances, weproposed that nitryl cyanide (NCNO2), a nearly nonpolarmolecule with a unique combination of two strongly electronegativeand polarized functional groups, is a novel fluorine-free replacementto be used as the insulating gas in green electrical grids. Atmosphericchemistry of NCNO2 has been investigated theoreticallyto assess its environmental impact if emitted into the atmosphere.Potential energy surfaces for the reaction of NCNO2 withOH in the presence of O-2 were calculated using the restrictedopen-shell complete basis set quadratic Becke3 and Gaussian-4 methodson the basis of the density functional (M06-2X) and couple-cluster(CCSD) optimized geometrical parameters. The oxidation of NCNO2 takes place via the nearly zero-barrier association of OHwith the cyano-C to form energy-rich adducts NC(OH)NO2,followed by C-N bond rupture to the major HOCN + NO2 and the minor HONO + NCO products. Interception of the adduct byO(2) can result in OH-regeneration together with furtherdegradation to CO and NO x . Moreover, photolysisof NCNO2 under tropospheric sunlight conditions might competewith OH-oxidation. The atmospheric lifetime and radiative efficiencyof NCNO2 were computed to be far less than those of eithernitriles or nitro compounds. The global warming potential of NCNO2 was estimated to be in the range of 0-5 for a 100year time horizon. However, the secondary chemistry of NCNO2 should be treated with caution in view of the production of NO x in the atmosphere.