Electronic Structures and OH-Induced Atmospheric Degradation of CF3NSF2: A Potential Green Dielectric Replacement for SF6.

Abstract

Electronic structures of [(trifluoromethyl)imino]sulfur difluoride (CF3NSF2) and degradation mechanisms by hydroxyl radical have been investigated using density functional theory (M06-2X), the complete basis set quadratic CBS-Q, and the explicitly correlated coupled-cluster methods [CCSD(T)-F12]. The d-function augmented correlation-consistent basis sets including triple- and quadruple-ξ were employed for the sulfur-containing species. It was found that CF3NSF2 exists as two conformations connected by the internal rotation of CF3 around the central NS bond. The distorted syn conformer is more stable than the symmetrical anti conformer. The nitrogen-sulfur link in CF3NSF2 was revealed to be predominantly ionic CF3N--+SF2 in structure rather than the conventional N═S double bond on the basis of natural bond orbital analysis. OH radical prefers to attach on the S atom of CF3NSF2 along the opposite direction of the S-F bond via a nucleophilic addition mechanism with a barrier of 2.9 kcal/mol whereas the ON association pathway is negligible. Although many product channels are thermodynamically favorable, none of them is kinetically accessible because of the significant barriers along the reaction routes. However, the degradation of CF3NSF2 by OH can be accelerated considerably in the presence of a single water molecule, which acts as a bridge for the consecutive proton migration within the floppy cyclic geometries. The half-life of CF3NSF2 was estimated to be 2.5 year, and the final products are exclusively CF3NH and SF2O. Theoretical calculation supports that CF3NSF2 is an environment-friendly green gas. It is worthy of testing its dielectric properties to replace SF6 for practical use.