Paola Antoniotti

Gas-phase ion chemistry of silane with ethane and ethyne

Abstract Silane–ethane and silane–ethyne systems have been studied by ion trap mass spectrometry and the variation of the abundances, with reaction time, of the ions containing silicon and carbon together in 5:1, 1:1 and 1:5 mixtures, have been reported. The best ion yield, which increases with the total pressure, is observed for 1:1 silane–ethyne mixture. Reaction mechanisms and rate constants of the first nucleation processes have been determined. In SiH 4 –C 2 H 2 systems, the formation of ions containing new SiC bonds occurs starting mainly from Si m H n + ions in the first steps, whereas the Si m C n H p + cluster species further reacts with high efficiency in processes with ethyne.

Gas phase ion chemistry in germane/ammonia, methylgermane/ammonia, and methylgermane/phosphine

Abstract Gaseous mixtures of germane or methylgermane with ammonia and methylgermane with phosphine have been studied by ion trap mass spectrometry. Rate constants of reactions of the primary ions and of the most important secondary ion species are reported, together with the calculated collisional rate constants and efficiencies of reaction. The GeH n + (n = 0–3) ions, formed by electron ionization of both GeH 4 and CH 3 GeH 3 , react with ammonia yielding, among others, the GeH n + (n = 2–4) ion family, which, in a successive and slow reaction with NH 3 , only give the unreactive ammonium ion. Also, the CH 3 GeH n + (n = 1, 2) species do not form Ge–N bonds, whereas secondary ions of germane, such as Ge 2 H 2 + , produce species containing germanium and nitrogen together. In the CH 3 GeH 3 /PH 3 mixture a great number of ions are formed with rather high rate constants from primary ions of both reagent molecules and from phosphorus containing secondary ions. GePH n + (n = 2–4) ions further react with methylgermane leading to cluster ions with increasing size such as Ge 2 PH n + and Ge 2 CPH n + . The experimental conditions favoring the chain propagation of ions containing Ge and N, or Ge and P, with or without C, important in the chemical vapor deposition of materials of interest in photovoltaic technology, are discussed.

Gas phase ion chemistry in silane/propane and silane/propene mixtures

Abstract The silane/propane and silane/propene gaseous mixtures have been investigated by ion trap mass spectrometry. The variations of ion abundances observed under different partial and total pressures are reported. The mechanisms of ion/molecule reactions have been elucidated by successive isolation steps. Moreover, the rate constants for the main processes have been experimentally measured and compared with the collisional rate constants to determine the reaction efficiencies. A great number of processes have been observed in SiH 4 /C 3 H 6 leading to the formation of silicon and carbon containing ions with high efficiency, whereas propane and silane give very few ion products with low efficiencies. Chain propagation in the SiH 4 /C 3 H 6 system gives clusters of increasing size, such as Si 2 C 2 H 7 + and Si 3 CH 7 + , with rather high efficiencies starting from silicon containing ions and neutral propene.

Gas phase ion chemistry and ab initio theoretical study of phosphine. I

Gas phase ion processes of phosphine have been studied by theoretical calculations and experimental techniques. Ab initio quantum chemical calculations have been performed on the ion/molecule reactions starting from P+ in PH3, as they have been observed by ion trapping. P+ gives P2Hn+ (n=1,2) product ions with loss of H2 or H in different pathways and also reacts in charge-exchange processes to form PH3+. The energies of transition structures, reaction intermediates, and final products, as well as their geometrical structures have been determined by theoretical methods. The initial step is formation of a triplet P2H3+ adduct of C3v symmetry (P–PH3+). A hydrogen atom can either be directly lost from the tetracoordinated phosphorus, or first undergo a shift to the other P atom (HP+–PH2), followed by P–H bond dissociation. Dissociation of H2 from P2H3+ can also occur from both the initial P–PH3+ and HP+–PH2 species yielding PPH+. The heats of formation of the P2Hn+ ionic species have also been computed and c...

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

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).

Gas-phase chemistry of ionized and protonated GeF4: a joint experimental and theoretical study.

The gas-phase ion chemistry of GeF(4) and of its mixtures with water, ammonia and hydrocarbons was investigated by ion trap mass spectrometry (ITMS) and ab initio calculations. Under ITMS conditions, the only fragment detected from ionized GeF(4) is GeF(3)(+). This cation is a strong Lewis acid, able to react with H(2)O, NH(3) and the unsaturated C(2)H(2), C(2)H(4) and C(6)H(6) by addition-HF elimination reactions to form F(2)Ge(XH)(+), FGe(XH)(2)(+), Ge(XH)(3)(+) (X = OH or NH(2)), F(2)GeC(2)H(+), F(2)GeC(2)H(3)(+) and F(2)GeC(6)H(5)(+). The structure, stability and thermochemistry of these products and the mechanistic aspects of the exemplary reactions of GeF(3)(+) with H(2)O, NH(3) and C(6)H(6) were investigated by MP2 and coupled cluster calculations. The experimental proton affinity (PA) and gas basicity (GB) of GeF(4) were estimated as 121.5 ± 6.0 and 117.1 ± 6.0 kcal mol(-1), respectively, and GeF(4)H(+) was theoretically characterized as an ion-dipole complex between GeF(3)(+) and HF. Consistently, it reacts with simple inorganic and organic molecules to form GeF(3)(+)-L complexes (L = H(2)O, NH(3), C(2)H(2), C(2)H(4), C(6)H(6), CO(2), SO(2) and GeF(4)). The theoretical investigation of the stability of these ions with respect to GeF(3)(+) and L disclosed nearly linear correlations between their dissociation enthalpies and free energies and the PA and GB of L. Comparing the behavior of GeF(3)(+) with the previously investigated CF(3)(+) and SiF(3)(+) revealed a periodically reversed order of reactivity CF(3)(+) < GeF(3)(+) < SiF(3)(+). This parallels the order of the Lewis acidities of the three cations.

Radiolysis of binary systems containing germanium and carbon hydrides

Abstract Radiolysis of the mixtures GeH4/C2H6 and GeH4/C3H8 have been studied. The decomposition of the parent molecules leads to solid and volatile products. The decomposition of GeH4, according to the composition of the mixtures, is 1.7–2.5 times larger than in pure GeH4. Also and hydrocarbons decompose 1.6–3.4 times more than in systems containing the pure reactants. The formation of the solid, a polymer containing Ge, C and H, has been attributed to a polymerization process initiated by the germylene-like species, while the gaseous products seem to derive from germyl-like species. The radical mechanism seems to prevail on the ionic.

Non-linear optical properties of β-D-fructopyranose calcium chloride MOFs: an experimental and theoretical approach

The second harmonic generation (SHG) properties of two MOFs, obtained from fructose and calcium chloride, were studied using a Non-Linear Optics Multimodal microscope. The first-order hyperpolarizability and the second-order susceptibility were calculated at the DFT level of theory. Moreover, a semi-classical approach to non-linearities in the optical behaviour was used in order to determine the features responsible for the SHG. The MOFs were synthesized both in ethanol and by solid–solid interaction, with a simple, rapid and low-cost methodology with no environmental impact, and were characterized with IR and RAMAN spectroscopy and both the single-crystal and powder X-ray diffraction. Both the metal–carbohydrate-based MOFs show an interesting SHG intensity: in particular, compound 1 shows an average SH intensity more than twice that of sucrose, in agreement with the theoretical results. A favourable combination of optical properties, transparency, thermal and chemical stability makes compound 1 a potential candidate for applications in electro-optics devices.

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

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 = 1–3). 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 SiH3+ are also “sink” species in our observed chemistry.

FSO+ and FSO2+ ions from ionised sulfur oxyfluorides: a computational investigation on the structure, stability, and thermochemistry

Abstract Singlet and triplet F–S–O+, F–O–S+, F–S(O)–O+, and FO–SO+ isomers have been investigated at the Coupled Cluster, G2, and G3 theoretical levels. At the CCSD(T)/aug-cc-pVTZ//CCSD/cc-pVDZ, the F–S–O+ isomer 1S (1A′) and the F–S(O)–O+ isomer 3S (1A1) resulted the global minima on the singlet surfaces, more stable than the corresponding triplet by ≈64 and 47 kcal mol−1, respectively. The G2 and G3 estimates of the enthalpies of formation of the various singlet and triplet FSO+ and FSO2+ isomers allow to identify the species observed from the photon and electron ionization of the simplest sulfur oxyfluorides as the ions 1S and 3S.