Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical study

Abstract

The ion-molecule reactions occurring in GeH(4)/NF(3), GeH(4)/SF(6), and GeH(4)/SiF(4) gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NF(x)(+) (x=1-3) react with GeH(4) mainly by the exothermic charge transfer, the open-shell Ge(+) and GeH(2)(+) undergo the efficient F-atom abstraction from NF(3) and form GeF(+) and F-GeH(2)(+) as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes Ge-F-NF(2)(+) and H(2)Ge-F-NF(2)(+), their subsequent crossing to the significantly more stable isomers FGe-NF(2)(+) and F-GeH(2)-NF(2)(+), and the eventual dissociation of these ions into GeF(+) (or F-GeH(2)(+)) and NF(2). The closed-shell GeH(+) and GeH(3)(+) are instead much less reactive towards NF(3), and the only observed process is the less efficient formation of GeF(+) from GeH(+). The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH(+). Passing from NF(3) to SF(6) and SiF(4), the average strength of the M-F bond increases from 70 to 79 and 142 kcal mol(-1), and in fact the only process observed by reacting GeH(n)(+) (n=0-3) with SF(6) and SiF(4) is the little efficient F-atom abstraction from SF(6) by Ge(+). Irrespective of the experimental conditions, we did not observe any ionic product of Ge-N, Ge-S, or Ge-Si connectivity. This is in line with the previously observed exclusive formation of GeF(+) from the reaction between Ge(+) and C-F compounds such as CH(3)F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF(+) and GeH(4).

Positive Ion Chemistry of SiH4/NF3 Gaseous Mixtures Studied by Ion Trap Mass Spectrometry

“…It is also of interest to compare the present results with those obtained recently from the study of GeH 4 /Nf 3 gaseous mixtures. 74 Both the SiH n + and GeH n + (n = 0-3) show a distinct preference for the fluorine atoms of Nf 3 . However, compared with the silicon cations, the germanium ions are, in general, much less reactive.…”

“…[67][68][69][70][71][72][73] We also make a brief comparison with our recently investigated positive ion chemistry occurring in GeH 4 /Nf 3 gaseous mixtures. 74 Experimental Silane (99.99% purity grade) and nitrogen trifluoride (99.99% purity grade) were purchased by SIAD (Bergamo, Italy) and Praxair (oevel, Belgium), respectively, and were dried by sodium sulphate before use. Helium (99.9999%) was purchased by SIAD and was used without further purification.…”

Gas‐phase reactions of XH3+ (X = C, Si, Ge) with NF3: a comparative investigation on the detailed mechanistic aspects

“…+ and NF 3 The products of the gas-phase reactions of CH 3 + , CD 3 + , SiH 3 + , [19] and GeH 3 + [18] with NF 3 observed by ITMS are listed in Table 1. Based on the available experimental or theoretical thermochemical data, [19,51] all the observed processes are predicted to be exothermic.…”

“…[18,19] Briefly, CH 4 (or CD 4 ), NF 3 , and buffer helium were introduced into the trap at pressures of ca 6.0 × 10 −7 and ca 1.0 × 10 −4 Torr (1 Torr = 133 Pa), respectively, empirically set so to maximize the abundance of the signals, and measured by a Bayard Alpert ion gauge. The nominal values were corrected for different sensitivity toward different gases, [31] and for a calibration factor which depends on the geometry of the instrument.…”

Positive Ion Chemistry of SiH4/GeF4 Gaseous Mixtures Studied by Ion Trap Mass Spectrometry and Ab Initio Calculations

“…the primary Nf x + (x = 1-3) react instead with SiH 4 mainly by charge transfer, even though additional products were observed which suggest the formation of intimate Positive ion chemistry of SiH 4 /GeF 4 gaseous mixtures studied by ion trap mass spectrometry and ab initio calculations reaction complexes. As a continuation of this study, and stimulated also by our current interest for the gas-phase chemistry of germanium-fluorine compounds, [51][52][53][54][55] we decided to use ion trap mass spectrometry (ITMS) and a high level of theory ab initio calculations to investigate the positive ion-molecule reactions occurring in SiH 4 /GeF 4 gaseous mixtures. These systems are also of applied interest when employed to deposit silicon-germanium thin films by plasma techniques.…”