Portal de Periódicos da CAPES

Gas-Phase Chemistry of the Sulfur Hexafluoride Fragment Ions SF n + ( n = 0−5) and SF n 2+ ( n = 2, 4). Ab Initio Thermochemistry of Novel Reactions of S +• and SF +

1998; American Chemical Society; Volume: 102; Issue: 27 Linguagem: Inglês

10.1021/jp980876g

1520-5215

Regina Sparrapan, Maria Anita Mendes, Isabel P. P. Ferreira, Marcos N. Eberlin, Christiano dos Santos, J. C. Nogueira,

Inorganic Fluorides and Related Compounds

A systematic study of the gas-phase chemistry of the major positively charged ions produced by 70 eV dissociative electron ionization of SF6, i.e., SFn+ (n = 0−5) and SFn2+ (n = 2, 4), has been performed via pentaquadrupole (QqQqQ) mass spectrometric experiments in conjunction with G2(MP2) ab initio calculations. Comparison, under exactly the same 15 eV collision conditions, of the SFn+ proclivities to dissociate by F loss was accomplished via a tandem-in-space three-dimensional MS2 scan. The experimental SFn+ dissociation proclivities were found to correlate perfectly with those expected from G2(MP2) dissociation thresholds. Ion/molecule reactions of mass-selected SFn+ and SFn2+ were performed with O2 and the oxygenated neutral gases H2O, CO, CO2, and N2O. The ions, under the very low energy (near zero) multiple collision conditions employed, undergo either dissociation by F loss or charge exchange, or participate in novel reactions that have been corroborated by both MS3 experiments and G2(MP2) ab initio thermochemistry. O-abstraction takes place in reactions of SF+ with O2 and CO, and of S+• with CO2 and O2, and the corresponding oxyions F−SO+ and SO+• are formed to great extents. CO-abstraction that yields ionized carbon oxysulfide (COS+•) also occurs to a minor extent in reactions of S+• with CO2. Reactions of SF+ with CO yields a minor COS+• product in a net sulfur cation (S+•) transfer reaction. Theory corroborates the experimental observations as the respective O-abstraction and S+• transfer reactions are predicted by G2(MP2) ab initio thermochemistry to be the most favorable processes.