Gas Phase Ion−Molecule Reactions in Phosphine/Silane Mixtures

Abstract

Phosphine/silane mixtures have been investigated by ion trap mass spectrometry, and reaction pathways together with rate constants of the main reactions are reported. Mechanisms of ion-molecule reactions have been elucidated by single and multiple isolation steps, and exact mass measurements have been performed by Fourier transform mass spectrometry. The SiH n + (n ) 0-3) ions react with phosphine to give SiPH n + (n ) 1-4) ions. These ions further react and yield SiP 2 H n + (n ) 2-5) and Si 2 PH n + (n ) 3-7) ions, which, in turn, react following different pathways with silane or phosphine to give Si 2 P 2 H n + (n ) 5, 6, 8) and Si 3 PH n + (n ) 5-7), respectively. Mixed SiPH n + (n ) 1-4) ions also originate from the PH n + (n ) 0, 1) phosphine primary ions, as well as from the P 2 H n + (n ) 0-3) secondary ions of phosphine. Protonation of phosphine from several ionic precursors is a very common process and yields the stable phosphonium ion, PH 4 + . Trends in total abundances of tertiary SiP 2 H n + (n ) 2-4) and Si 2 PH n + (n ) 3-7) ions as a function of reaction time for different PH 3 /SiH 4 pressure ratios show that excess of silane favors the nucleation of mixed Si-P ions. The mechanism and energetics of the reaction of Si + with PH 3 have been investigated by ab initio calculations, and the most stable structure of the SiPH + product, with a hydrogen bridge between silicon and phosphorus, has been identified.

Gas phase ion chemistry and ab initio theoretical study of phosphine. III. Reactions of PH2+ and PH3+ with PH3

“…[3][4][5][6] The pressures were read by a Bayard-Alpert ionization gauge and were typically 2 -5ϫ10 Ϫ7 Torr for phosphine and about 5 ϫ10 Ϫ4 Torr for helium. The real pressure in the trap was calculated considering the relative sensitivity of the ion gauge with respect to different gases 8 and a calibration factor for the geometry of the instrument.…”

“…The real pressure in the trap was calculated considering the relative sensitivity of the ion gauge with respect to different gases 8 and a calibration factor for the geometry of the instrument. 5 The scan modes for ion/molecule reaction experiments, in which reaction mechanisms and rate constants are determined, have been previ-ously described in detail together with the calculation procedures. [3][4][5][6] In kinetic experiments, isolation of the precursor ions was generally obtained by a superimposition of radio frequency ͑rf͒ and direct current ͑dc͒ voltages.…”

“…5 The scan modes for ion/molecule reaction experiments, in which reaction mechanisms and rate constants are determined, have been previ-ously described in detail together with the calculation procedures. [3][4][5][6] In kinetic experiments, isolation of the precursor ions was generally obtained by a superimposition of radio frequency ͑rf͒ and direct current ͑dc͒ voltages. In some cases, experiments were also performed in which ions were selectively stored by resonance ejection, without any dc voltage which could add energy to the ions under examination.…”

“…[3][4][5] Understanding the nature of ion/molecule clustering reactions is an extremely important problem in the field of cluster chemistry, in particular the investigation of the chain propagation and the consequent cluster nucleation and growth.…”

Gas‐Phase Ion Chemistry of Silicon‐Containing Molecules†This article is dedicated to Saul Patai.

“…The ion molecule reactions that occur in mixtures of SiH 4 and PH 3 have recently been described 115 . As in the aforementioned cases, the main reaction channels for the formation of larger-sized clusters from SiH n C cations (n D 0 3) and PH 3 , and from the reactions of PH x C cations (n D 0 3) with SiH 4 , correspond to the addition of the neutral molecule and dissipation of the excess energy via loss of a hydrogen molecule.…”