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 2 ), 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 2 has been investigated theoretically to assess its environmental impact if emitted into the atmosphere. Potential energy surfaces for the reaction of NCNO 2 with OH in the presence of O 2 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 2 takes place via the nearly zero-barrier association of OH with the cyano-C to form energy-rich adducts NC(OH)NO 2 , followed by C-N bond rupture to the major HOCN + NO 2 and the minor HONO + NCO products. Interception of the adduct by O 2 can result in OH-regeneration together with further degradation to CO and NO x . Moreover, photolysis of NCNO 2 under tropospheric sunlight conditions might compete with OH-oxidation. The atmospheric lifetime and radiative efficiency of NCNO 2 were computed to be far less than those of either nitriles or nitro compounds. The global warming potential of NCNO 2 was estimated to be in the range of 0-5 for a 100 year time horizon. However, the secondary chemistry of NCNO 2 should be treated with caution in view of the production of NO x in the atmosphere.