Theoretical Study of the Anthropogenic Greenhouse Gas ( SF5CF3) and Analysis of the Reaction of SF6 with CF3-

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)SF5CF3 was recently detected in the earth's atmosphere. This has lead to various experimental and theoretical studies aimed at establishing the properties of this molecule, from which to understand how it is formed, how it may impact on the atmosphere (it is a powerful greenhouse gas), and how it may be destroyed in the atmosphere. SF5CF3 is chemically very inert, and is not destroyed in the troposhere. Theoretical calculations using effective core potential (ECP) based on high-level methods -QCISD(T), were performed for molecular systems related to SF5CF3. Existing values for the S-C bond dissociation energy in SF5CF3 span a wide range, from estimates of about 200 to 300 kJ mol(-1), obtained from theoretical calculations on SF5CF3 using the DFT, G2, and G3 protocols, to 390 +/- 45 kJ mol(-1) derived from experimental studies of the photoionisation of SF5CF3. At the QCISD(T)/ECP+GCM (generator coordinate method) level, the dissociation energy -D-O(SF5-CF3, 0 K), is 274.7 kJ mol(-1). In addition to calculations on individual molecules, the reactions of SF6 with CF3- were studied. The first objective was to locate the reactant ion-molecule complex, the transition state, and the product ion-molecule complex for each of these systems. On the basis of literature thermochemistry, the reaction of SF6 with CF3-, in which the CF3- reactant anion abstracts F+ from SF6 to leave SF5-, is highly exothermic (-343 kJ mol(-1)). At the QCISD(T)/ECP+ GCM level gives a value of -377.6 kJ mol(-1). (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1555-1561, 201111141858SI15551561Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP