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

In view of the significant greenhouse effect of sulfur hexafluoride and the potential biotoxic hazard of perfluorinated substances, we proposed that nitryl cyanide (NCNO), a nearly nonpolar molecule with a unique combination of two strongly electronegative and polarized functional groups, is a novel fluorine-free replacement to be used as the insulating gas in green electrical grids. Atmospheric chemistry of NCNO has been investigated theoretically to assess its environmental impact if emitted into the atmosphere. Potential energy surfaces for the reaction of NCNO with OH in the presence of O were calculated using the restricted open-shell complete basis set quadratic Becke3 and Gaussian-4 methods on the basis of the density functional (M06-2X) and couple-cluster (CCSD) optimized geometrical parameters. The oxidation of NCNO takes place via the nearly zero-barrier association of OH with the cyano-C to form energy-rich adducts NC(OH)NO, followed by C-N bond rupture to the major HOCN + NO and the minor HONO + NCO products. Interception of the adduct by O can result in OH-regeneration together with further degradation to CO and NO. Moreover, photolysis of NCNO under tropospheric sunlight conditions might compete with OH-oxidation. The atmospheric lifetime and radiative efficiency of NCNO were computed to be far less than those of either nitriles or nitro compounds. The global warming potential of NCNO was estimated to be in the range of 0-5 for a 100 year time horizon. However, the secondary chemistry of NCNO should be treated with caution in view of the production of NO in the atmosphere.