THEORETICAL AND EXPERIMENTAL-STUDY OF THE GAS-PHASE REACTIONS OF PFN-BASES - A NOVEL ROUTE TO PHOSPHORUS IONS PRESENT IN INTERSTELLAR CLOUDS( (N=1, 2) IONS WITH N)

The reactivity of PFn+ (n = 1, 2) cations toward n-type bases, such as H2O, CH3OH, and NH3, has been investigated using Fourier-transform io n cyclotron resonance (FT-ICR) mass spectrometry. Both phosphorus ions attack the n-center of the selected bases, yielding the corresponding excited onium intermediates, which undergo extensive prototropic rear rangements before fragmenting with formal losses of H and HF (with H2O and NH3) or HF, CH3, and CH3F (with CH3OH). Ab initio molecular orbit al calculations at the G2 level of theory have been used to study the structures, the relative stability, and the proton loss energies of th e ionic species involved in these reactions. The G2 [PF, H2O](+) and [ PF, NH3](+) potential energy profiles conform well with the FT-ICR rea ction kinetics. Unequivocal assignment of the structure and the multip licity of several ionic species obtained from the title reactions and potentially involved in the formation of phosphorus-containing molecul es in outer space, i.e. (PO)H+, (FPO)H+, (PNH)H+, and (FPNH)H+, is all owed by a comparison of their G2-calculated proton loss energies with the experimental protonation enthalpies, measured in the FT-ICR instru ment with the bracketing technique. The emerging picture has been comp ared with previous theoretical data concerning strictly related specie s wherein the phosphorus atom is replaced by nitrogen.