Gas-phase ion chemistry of Si+ and NF3:: An experimental and theoretical study

The study of the gas-phase reactions of the Si+ ions with nitrogen trifluoride (NF3) was performed by quadrupole ion trap mass spectrometry and ab initio calculations. Experimental results display a thermodynamically favoured reaction cascade starting from the reactants corresponding to multiple fluorine abstraction, which ultimately yields neutral fluorosilane by fluoride abstraction. A parallel, slightly endothermic channel is observed starting from the reactants and generating the NF2+ and SiF products. The study of the potential energy hypersurface of the Si+(P-2) + NF3 system evidenced the initial formation of the N-coordinated Si+-NF3 adduct. Subsequent rearrangements and atom migrations lead to the FSi+-NF2 isomer, whose dissociation yields SiF+ and NF2 as products. Theoretical energy profiles show that this pathway is strongly exothermic (about - 100 kcal mol(-1)) and that the dissociation of the FSi+-NF2 species to the endothermic (+6 kcal mol(-1)) channel products (NF2+ and SiF) is extremely unlikely for ground-state reactants. (C) 2006 Elsevier B.V. All rights reserved.