Negative gas‐phase ion chemistry of silane: a quadrupole ion trap study

Abstract

Silicon clusters are of considerable interest for their importance in astrophysics and chemical vapour deposition processes, as well as from a fundamental point of view. Here, we present a quadrupole ion trap study of the self-condensation ion/molecule reactions of anions of silane. In the high-pressure regime, several ion clusters are formed with increasing size: the largest ions detected are Si5Hn- (n = 0-3). Selective ion isolation and storage allowed detection of the main reaction sequences occurring in the reacting system. The most frequent condensation step is followed by single or multiple dehydrogenation, this latter being particularly observed for the high-mass reactant ions. As a consequence, the most abundant ions in the mass spectra are those with a low content of hydrogen, namely Si2H-, Si3H-, and Si4H-. These results are discussed with reference to literature data on silicon cluster anions and related systems.

Syntheses of Trisila Analogues of Allyl Chlorides and Their Transformations to Chlorocyclotrisilanes, Cyclotrisilanides, and a Trisilaindane

“…Contrary to our expectations, the anticipated trisila analogue to allyl lithiums could not be observed. Instead, the first example of an anionic cyclotrisilanide , was formed as the only detectable product and isolated as its lithium salt 7b ·Li + ·Et 2 O in 50% yield. The structure determination by single-crystal X-ray diffraction (Figure ) reveals the presence of a close contact ion pair, in which Li1 strongly coordinates to the negatively charged silicon atom and shows additional contacts to Si2 and one ipso -carbon atom (Si1−Li1 258.0(4), Si2−Li1 289.8(4), Li1−C31 245.5(4) pm).…”

Multiple dehydrogenation reactions of negative ions in low pressure silane plasma chemistry

“…Conversely, in section 6, the heavier silanions are first modelled by a binomial distribution of dehydrogenation reactions, before convolution with the silicon isotopes, in order to compare with the measured mass spectrum in section 7. The principal result in the conclusions is that multiple dehydrogenation reactions, as directly observed by Operti et al [35], can accurately account for the measured mass spectrum up to at least 800 amu. This suggests that silanion-neutral nucleation models could be improved by including multiple deydrogenation reactions.…”

“…In the pure silane, 0.1 mbar plasma of this work, silicon hydride anion mass spectra are interpreted in terms of iterative anion-silane reactions, involving release of one, or two, hydrogen molecules. Such 'multiple dehydrogenation' has been directly observed by Operti et al [2006 Rapid Commun. Mass Spectrom.…”

Ion/Molecule reactions in SiH4/H2S and GeH4/H2S mixtures

“…With regards to silane ions, the only primary ions, which were abundant enough to be isolated, i.e. the SiH 3 − ions, were unreactive toward H 2 S. The most abundant ions formed in silane self‐condensation reactions previously studied69 are the Si n H − ( n = 2–5) ions, which did not display any reaction with H 2 S. Selection and storage of the quite abundant Si 2 H 5 − ions yield the Si 2 SH 5 − ions, by condensation followed by H 2 loss ( k = 6.4 × 10 −11 cm 3 molecule −1 s −1 ). Hence, ion isolations do not account for formation of the HS − and SiSH 3 − ions, which were observed to be quite abundant in the mixture with ionized silane.…”