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

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.