Abstract

European Journal of Mass Spectrometry
Volume 15 Issue 2, Pages 209–220 (2009)
doi: 10.1255/ejms.950

Positive ion chemistry of SiH₄/NF₃ gaseous mixtures studied by ion trap mass spectrometry

Paola Antoniotti,^a Lorenza Operti,^a Roberto Rabezzana,^a Francesca Turco,^a Stefano Borocci^b and Felice Grandinetti^b,*
aDipartimento di Chimica Generale e Chimica Organica and NIS Centre of Excellence, Università di Torino, C.so M. D'Azeglio 48, 10125 Torino, Italy
^bDipartimento di Scienze Ambientali, Università della Tuscia, L.go dell' Università , s.n.c., 01100 Viterbo, Italy. E-mail: fgrandi@unitus.it

The positive ion chemistry occurring in silane/nitrogen trifluoride gaseous mixtures has been investigated by ion trap mass spectrometry. Reaction sequences and rate constants have been determined for the processes involving the primary ions SiH_n⁺ (n = 0–3) and NF_x⁺ (x = 1–3) and the secondary ions obtained from their reactions with SiH₄ and NF₃. The SiH_n⁺ efficiently react with NF₃ and undergo cascades of abstraction and scrambling reactions which form the fluorinated and perfluorinated cations SiHF_m⁺ (m = 1, 2), SiH₂F⁺ and SiF_x⁺ (x = 0–3). Fluorinated Si₂-clusters such as Si₂H₂F⁺, Si₂H₃F⁺ and Si₂H₅F⁺ were also observed. The reaction of both SiH₃⁺ and SiH₂F⁺ with NF₃ produces the elusive fluoronitrenium ion NHF⁺. Any NF_x⁺ reacts with SiH₄ mainly by charge transfer. Additional ionic products are, however, observed which suggest intimate reaction complexes. Worth mentioning is the formation of SiNH₂⁺ from the reaction of both NF⁺ and NHF⁺ with SiH₄. The primary ions NF₂⁺ and SiH₂⁺ are also “sink” species in our observed chemistry.

Keywords: cationic silicon fluorides, gas-phase ion chemistry, ion trap mass spectrometry, nitrogen trifluoride, silane

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