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

Abstract

The gas-phase reaction of CH(3)(+) with NF(3) was investigated by ion trap mass spectrometry (ITMS). The observed products include NF(2)(+) and CH(2)F(+). Under the same experimental conditions, SiH(3)(+) reacts with NF(3) and forms up to six ionic products, namely (in order of decreasing efficiency) NF(2)(+), SiH(2)F(+), SiHF(2)(+), SiF(+), SiHF(+), and NHF(+). The GeH(3)(+) cation is instead totally unreactive toward NF(3). The different reactivity of XH(3)(+) (X = C, Si, Ge) toward NF(3) has been rationalized by ab initio calculations performed at the MP2 and coupled cluster level of theory. In the reaction of both CH(3)(+) and SiH(3)(+), the kinetically relevant intermediate is the fluorine-coordinated isomer H(3)X-F-NF(2)(+) (X = C, Si). This species forms from the exoergic attack of XH(3)(+) to one of the F atoms of NF(3) and undergoes dissociation and isomerization processes which eventually result in the experimentally observed products. The nitrogen-coordinated isomers H(3)X-NF(3)(+) (X = C, Si) were located as minimum-energy structures but do not play an active role in the reaction mechanism. The inertness of GeH(3)(+) toward NF(3) is also explained by the endoergic character of the dissociation processes involving the H(3)Ge-F-NF(2)(+) isomer.

Gas‐phase reactions of SiHn+ (n = 1,2) with NF3: A computational investigation on the detailed mechanistic aspects

“…The comparison of the present results with those concerning the reactions between Si þ [33] and SiH 3 þ [35] and NF 3 allow to appreciate the effect of the electronic structure and of the spin multiplicity of the cation on the mechanistic aspects of the reactions between SiH n þ and NF 3 the N-coordinated complexes Si þ -NF 3 and H 2 Si þ -NF 3 , which eventually evolve into the F-abstraction products SiF þ þ NF 2 and H 2 SiF þ þ NF 2 . The latter process involves in particular the passage through a conical intersection, which allows the isomerization of H 2 Si þ -NF 3 into H 2 Si-F þ (NF 2 ), and the eventual dissociation of this ion into its constituting fragments.…”

“…The comparison of the present results with those concerning the reactions between Si þ [33] and SiH 3 þ [35] and NF 3 allow to appreciate the effect of the electronic structure and of the spin multiplicity of the cation on the mechanistic aspects of the reactions between SiH n þ and NF 3 (n ¼ 0-3). Thus, both the singlet, closed-shell SiH þ and SiH 3 þ attach exclusively the F atom of NF 3 , so to form the F-coordinated complexes HSi-F-NF 2 þ and H 3 Si-F-NF 2 þ .…”

“…[36][37][38][39][40] The SiH n þ (n ¼ 0-3) react with NF 3 so to form ionic and/or neutral products with SiAF bonds. [33,35] Although the formation of SiF þ from the reaction between Si þ and NF 3 involves the intermediacy of the N-coordinated isomer Si-NF 3 þ , all the six ionic products observed from the reaction between SiH 3 þ and NF 3 arise from the dissociation and/or rearrangement of the F-coordinated isomer H 3 Si-F-NF 2 þ , and no evidence was obtained for the kinetic role of the N-coordinated complex H 3 Si-NF 3 þ . [41] More interesting was the observation that the nature of the observed processes reflects the spin multiplicity of the cation.…”

“…More recently, ion trap mass spectrometry (ITMS) and ab initio calculations were used to study the reactions occurring in ionized mixtures of SiH 4 and NF 3 . [33][34][35] These systems are also of applied interest when used to deposit fluorinated electronic and optoelectronic materials by chemical vapor deposition techniques. [36][37][38][39][40] The SiH n þ (n ¼ 0-3) react with NF 3 so to form ionic and/or neutral products with SiAF bonds.…”

“…Theoretical calculations were also performed to investigate the mechanisms of the reactions of Si þ and SiH 3 þ with NF 3 . [33,35] Although the formation of SiF þ from the reaction between Si þ and NF 3 involves the intermediacy of the N-coordinated isomer Si-NF 3 þ , all the six ionic products observed from the reaction between SiH 3 þ and NF 3 arise from the dissociation and/or rearrangement of the F-coordinated isomer H 3 Si-F-NF 2 þ , and no evidence was obtained for the kinetic role of the N-coordinated complex H 3 Si-NF 3 þ . To further appreciate the influence of the electronic structure and the spin multiplicity of the cation on the reactions between SiH n þ (n ¼ 0-3) and NF 3 , we explored the mechanisms of the processes involving SiH þ and SiH 2 þ .…”