Characterization of an argon-hydrogen microwave discharge used as an atomic hydrogen source. Effect of hydrogen dilution on the atomic hydrogen production

This work is devoted to the study of an argon-hydrogen microwave plasma used as an atomic hydrogen source. Our attention has focused on the effect of the hydrogen dilution in argon on atomic hydrogen production. Diagnostics are performed either in the discharge or in the post-discharge using emission spectroscopy (actinometry) and mass spectrometry. The agreement between actinometry and mass spectrometry diagnostics proves that actinometry on the Ha(656.3 nm) and Hβ(486.1 nm) hydrogen Balmer lines can be used to measure the relative atomic hydrogen density within the microwave discharge. Results show that the atomic hydrogen density is maximum for a gas mixture corresponding to the partial pressure ratioP _{H 2}/P _Ar range between 1.5 and 2. The variation of atomic hydrogen density can be explained by a change of the dominant reactive mechanisms. At a low hydrogen partial pressure the dominant processes are the charge transfers with recombinations between Ar⁺ and H₂ which lead to ArH⁺ and H ₂ ⁺ ion formation. Both ions are dissociated in dissociative electron attachment processes. At a low argon partial pressure the electron temperature and the electron density decrease with increasing partial pressure ratio. The dominant mechanisms become direct reactions between charged particles (e, H⁺, H ₂ ⁺ , and H ₃ ⁺ ) or excited species H(n=2) with H₂ producing H atoms.     

Absorption spectra of SiCl4, Si2Cl6, SiF3CH3 and GeF4 in the VUV region

In the range 110–200 nm the absorption features of Si₂Cl₆ closely resemble those of SiCl₄ and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron. Two diffuse bands in the SiF₃CH₃ absorption are also assigned to Rydberg excitations. The spectrum of GeF₄ shows a broad band considered to be a valence excitation of the outermost orbital. The emission of the SiCl₂ (ùB₁→X̃¹A₁) transition was found in the photoexcitation of Si₂Cl₆.     

Structure and fragmentations of [C3H7S]+ ions

The principal fragmentation reactions of metastable [C₃H₇S]⁺ ions are loss of H₂S and C₂H₄. These reactions and the preceding isomerizations of [C₃H₇S]⁺ ions with six different initial structures were studied by means of labelling with ¹³C or D. From the results it is concluded that the loss of H₂S and C₂H₄ both occur at least mainly from ions with the structure [CH₃CH₂CH? SH]⁺ or from ions with the same carbon sulfur skeleton, with the exception of the ions with the initial structure [CH₃CH₂S? CH₂]⁺, which partly lose C₂H₄ without a preceding isomerization. For all ions, more than one reaction route leads to [CH₃CH₂CH?SH]⁺. It is concluded that the loss of H₂S is at least mainly a 1,3-elimination from the [CH₃CH₂CH?SH]⁺ ions. Both decomposition reactions are preceded by extensive but incomplete hydrogen exchange.     

Bildung siliciumorganischer Verbindungen. 111. Die Hydrierung Si-chlorierter,C-spiroverbrückter 2,4-Disilacyclobutane mit LiAlH4 und iBu2AlH. Der Zugang zum Si8C3H20

Formation of Organosilicon Compounds. 111. The Hydrogenation of Si-chlorinated, C-spiro-linked 2,4-Disilacyclobutanes with LiAlH₄ or iBu₂AlH. The Access to Si₈C₃H₂₀ The hydrogenation of Si-chlorinated, C-spiro-linked 2,4-disilacyclobutanes containing C(SiCl₃)₂ terminal groups with LiAlH₄ in Et₂O proceeds under complete cleavage of the fourmembered rings and under elimination of one SiH₃ group. Such, Si₈C₃Cl₂₀ 4 forms (H₃Si)₂CH? SiH₂? CH(SiH₃)? SiH₂? CH(SiH₃)₂ 4 α, and even Si₈C₃H₂₀ 4a with LiAlH₄ forms 4 α. The hydrogenation of related compounds containing however CH(SiCl₃) terminal groups similarly proceeds under ring cleavage but no SiH₃ groups are eliminated. Such, (Cl₃Si)CH(SiCl₂)₂CH(SiCl₃) 41 forms (H₃Si)₂CH? SiH₂? CH₂(SiH₃) 41 α. However, in reactions with iBu₂AlH in pentane neither the disilacyclobutane rings are cleaved nor are SiH₃ groups eliminated. Only by this method Si₈C₃H₂₀ is accessible from 4 , Si₆C₂H₁₆ 3a from Si₆C₂Cl₁₆ 3 and Si₄C₂H₁₂ 41a from 41 . C(SiCl₃)₄ cleanly produces C(SiH₃)₄. Based on the knowledge about the different properties of LiAlH₄ and iBu₂AlH in hydrogenation reactions of disilacyclo-butanes it was possible to elucidate the composition and the structures of the hydrogenated derivatives of the product mixture from the reaction of MeCl₂Si? CCl₂? SiCl₃ with Si(Cu) [1] and to trace them back to the initially formed Si chlorinated disilacyclobutanes Si₆C₂Cl₁₅Me 34 , Si₆C₂Cl₁₄Me₂ 35 , Si₈C₃Cl₁₉Me 36 and Si₈C₃Cl₁₈Me₂ 37 . Compound 4a forms colourless crystals of space group P1 with a = 799.7(6), b = 1263.6(12), c = 1758.7(14) pm, α = 103.33(7)°, β = 95.28(6)°, γ = 105.57(7)° and Z = 4.     

SiCl 3 + and SiCl+ affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase

Cluster ions, Py₁SiCl ₃ ⁺ Py₂ and Py₁SiCl⁺Py₂, where Py₁ and Py₂ represent substituted pyridines, formed upon reactive collisions of mass-selected SiCl ₃ ⁺ or SiCl⁺ cations with a mixture of pyridines, are shown to have loosely bound structures by multiple stage mass spectrometry experiments in a pentaquadrupole mass spectrometer. The fragment ion abundance ratio, ln([Py₁SiCl _n ⁺ ]/[Py₂SiCl _n ⁺ ]) (n=1 or 3) is used to estimate the relative SiCl ₃ ⁺ or SiCl⁺ affinities of the constituent pyridines by the kinetic method. In the case of clusters comprised of meta- and/or para-substituted pyridines (unhindered pyridines), the SiCl ₃ ⁺ and SiCl⁺ affinities are shown to display excellent linear correlations with the proton affinities (PAs). On the assumption that the effective temperatures of the SiCl ₃ ⁺ - and SiCl⁺-bound dimers are 555 K (i. e., the same as those of the corresponding Cl⁺-bound dimers), SiCl ₃ ⁺ and SiCl⁺ affinities of the substituted pyridines, relative to pyridine, are estimated to be 3-MePy (2.1 kcal/mol), 4-MePy (3.2 kcal/mol), 3-EtPy (3.7 kcal/mol), 4-EtPy (4.2 kcal/mol), 3,5-diMePy (4.8 kcal/mol), and 3,4-diMePy (5.4 kcal/mol). The SiCl ₃ ⁺ and SiCl⁺ cation affinities are related to the proton affinities by the expressions: relative (SiCl ₃ ⁺ ) affinity = 0.95 ΔPA and relative (SiCl⁺) affinity = 0.60 ΔPA. The smaller constant in the relationship between the relative SiCl affinity and the relative proton affinity is the result of weaker bonding. Steric effects between the ortho-substituted alkyl group and the central SiCl ₃ ⁺ cation reduce the SiCl ₃ ⁺ affinities of dimers that contain ortho-substituted pyridines. The magnitude of the steric acceleration of fragmentation is used to measure a set of gas-phase steric parameters (S ^k). The steric effects in the SiCl ₃ ⁺ dimers are similar in magnitude to those in the corresponding Cl⁺-bound dimers but weaker than those produced by the bulky [OCNCO]⁺ group. An inverted steric effect is observed in those SiCl⁺-bound dimers that incorporate ortho-substituted pyridines and is ascribed to auxiliary Si-H-C bonding, which stabilizes the ortho-substituted pyridine-SiCl⁺ bond. This auxiliary bonding appears to correspond to agostic bonding, which is well characterized in solution and occurs in competition with steric effects that weaken the pyridine-SiCl⁺ interaction. Ion-molecule reactions of pyridines with halosilicon radical cations SiCl ₂ ⁺ and SiCl ₄ ⁺ as well as alkylated halosilicon cations Si(CH₃)₂Cl⁺ and Si(CH₃)Cl ₂ ⁺ also are investigated. In these cases, charge exchange and associated reactions are the main reaction channels, and clustering is not observed.     

Quenching of the OH and nitrogen molecular emission by methane addition in an Ar capacitively coupled plasma to remove spectral interference in lead determination by atomic fluorescence spectrometry

A new method is proposed to remove the spectral interference on elements in atomic fluorescence spectrometry by quenching of the molecular emission of the OH radical (A²Σ⁺ → X²Π) and N₂ second positive system (C³Π_u → B³Σ_g) in the background spectrum of medium power Ar plasmas. The experiments were carried out in a radiofrequency capacitively coupled plasma (275 W, 27.12 MHz) by CH₄ addition. The quenching is the result of the high affinity of OH radical for a hydrogen atom from the CH₄ molecule and the collisions of the second kind between nitrogen excited molecules and CH₄, respectively. The decrease of the emission of N₂ second positive system in the presence of CH₄ is also the result of the deactivation of the metastable argon atoms that could excite the nitrogen molecules. For flow rates of 0.7 l min^− 1 Ar with addition of 7.5 ml min^− 1 CH₄, the molecular emission of OH and N₂ was completely removed from the plasma jet spectrum at viewing heights above 60 mm. The molecular emission associated to CH and CH₂ species was not observed in the emission spectrum of Ar/CH₄ plasma in the ultraviolet range. The method was experimented for the determination of Pb at 283.31 nm by atomic fluorescence spectrometry with electrodeless discharge lamp and a multichannel microspectrometer. The detection limit was 35 ng ml^− 1, 2–3 times better than in atomic emission spectrometry using the same plasma source, and similar to that in hollow cathode lamp microwave plasma torch atomic fluorescence spectrometry.     

Differentiation of isomeric oxygenated adsorbates using low-energy ion/surface collisions

Reactive scattering of polyatomic ions in the hyperthermal collision energy range (<100 eV) is used to distinguish isomeric oxygenated adsorbates and to quantify their relative amounts when co-adsorbed at a surface. The self-assembled monolayers (SAMs) of interest are constructed from HO-terminated, CH₃O-terminated, and CH₃CH₂O-terminated dialkyl disulfides. Projectile ions used for ion/surface scattering experiments include CF₃⁺, SiCl₃⁺, and the molecular ion of pyridine, C₅H₅N√⁺. Each of these ions exhibits a unique scattered ion profile upon collision with the SAM monolayer surfaces, and so provides different information about the surfaces. Hydrogen atom abstraction by the C₅H₅N√⁺ ion is more prominent at the CH₃CH₂O- and CH₃O-terminated surfaces than the HO-terminated surface, while collisions of SiCl₃⁺ yield reactively scattered products which reflect the chemical composition of these surfaces. For instance, SiCl₂OH⁺ and SiCl₂OCH₃⁺ are scattered from the HO-terminated and CH₃O-terminated surfaces, respectively. Ion/surface collisions involving the CF₃⁺ ion produce chemically sputtered ions from the oxygenated adsorbates, which are valuable for quantitation of those groups. Preferential sputtering of the CH₃O-terminated versus the HO-terminated SAM surface is ascribed to favored thermochemistry and the more accessible CH₃O-terminated adsorbate. Fundamental ion/surface scattering processes, such as inelastic collisions leading to surface-induced dissociation (SID), ion/surface reaction, and chemical sputtering are examined over a range of collision energies for each of the ion/surface types mentioned, and their value in surface analysis is demonstrated.     

Fragmentation behavior of Si2Cln+ cations (n = 1—6)

Sector-field mass spectrometry was used to probe the fragmentation patterns of the cationic silicon chlorides Si₂Cl_n ⁺ (n = 1—6). For almost all Si₂Cl_n ⁺ ions, Si—Si fragmentation predominates the Si—Cl bond cleavage both in the metastable ion and collisional activation mass spectra. Analysis of the fragmentation patterns indicates that the long-lived radical cation Si₂Cl₆ ^·+ corresponds to a complex [SiCl₂·SiCl₄]^·+ rather than the intact molecular ion of hexachlorodisilane. The behavior of Si₂Cl₅ ⁺ is consistent with the formation of the (trichlorosilyl)dichlorosilyl cation Cl₃SiSICl₂ ⁺. Structural aspects are also discussed for the other Si₂Cl_n ⁺ species. A semi-quantitative analysis of the fragmentation patterns in conjunction with the literature thermochemistry data was used to estimate some thermochemical properties of the Si₂Cl_n ⁺ cations.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.     

Quadrupole mass spectrometric study of positive ions from RF plasmas of pure CH4, CH4/H2, and CH4/Ar systems

Quadrupole mass spectrometry has been employed to characterize the ionic species in the discharges of pure CH₄, CH₄/H₂, and CH₄/Ar systems. For pure methane, the major positive ions in the discharge at low pressure (e.g., 0.15 torr) are CH ₃ ⁺ , C₂H ₃ ⁺ , CH ₂ ⁺ , C₂H ₂ ⁺ , CH ₄ ⁺ , C₂H ₄ ⁺ , and C₂H ₅ ⁺ at high pressure (e.g., 0.5 torr) the major ions are CH ₃ ⁺ , C₂H ₃ ⁺ , C₂H ₅ ⁺ , C₃H ₃ ⁺ , C H₃H ₇ ⁺ , C₄H ₇ ⁺ , C₅H ₇ ⁺ , C₆H ₅ ⁺ , and C₇H ₇ ⁺ . The relative abundances of C₁ ions decrease with increasing pressure, whereas those of higher-order ions increase with pressure. For 5% CH₄ + 95% H₂ mixture, in addition to those sampling from the pure methane plasma at the lower pressure, H _n ⁺ ions have also been detected. For 5% CH₄ +95% Ar mixture, the principal ions are CH ₃ ⁺ , CH ₂ ⁺ , CH⁺, CH ₅ ⁺ , Ar⁺, and ArH⁺; the ions containing more than two carbon atoms are negligible. In these discharges, the CH ₃ ⁺ and C₂H ₃ ⁺ are the most important positive ions in C₁ and C₂ ions, respectively. The ions detected are believed to come from the sheath between the electrode and the luminous plasma, and have high kinetic energy. An ion-molecule reaction mechanism is proposed which can well explain the observed main features of ionic products.Died June 1, 1991.     

Hydrogen atom yield in RF and microwave hydrogen discharges

The hydrogen atom yield in pure-H₂ RF and microwave-sustained discharges is investigated both theoretically and experimentally. A particle balance model is developed that provides the concentrations of the H, H₂, H⁺, H ₂ ⁺ , and H ₃ ⁺ species. It is also shown that an approximate solution of this model is adequate for calculating the concentration of H atoms (required, for instance, in diamond film deposition) in the 0.1–10 torr range. Next, the validity of the actinometry technique applied to the determination of the H-atom density in pure-H₂ discharges is examined. Using this diagnostic, it is observed that the H-atom concentration decreases when the vessel wall temperature increases, owing to the increased efficiency of atomic hydrogen recombination on the wall. To overcome this effect, the discharge tube wall is cooled off with dimethyl polysiloxane, a low-loss dielectric liquid. It improves significantly the H-atom concentration at 2450 MHz provided the pressure is typically below a few torr and the power density is not too high.     

The ions [CH3S]+, [C2H5S]+ and [CH3O]+ formed by electron-impact

The mass spectra of deuterated species shows that both the isomeric ions [CH₂?SH]⁺ and [CH₃? S]⁺ are formed in the ratio 2:1 from CH₃SH; the ions [CH₃CH?SH]⁺ and [CH₃CH₂S]⁺ in the ratio 0·8:1 from CH₃CH₂SH; and [CH₂?OH]⁺ and [CH₃? O]⁺ in the ratio 6·7:1 from methanol. The heats of formation of [CH₃S]⁺ and [C₂H₅S]⁺ are of the order of 222 and 203 Kcal.mole^?1 respectively. The isomeric ions cannot be distinguished on thermodynamic grounds.     

A Density Functional Theory Study on the Effect of Zero‐Point Energy Corrections on the Methanation Profile on Fe(100)

The thermodynamics and kinetics of the surface hydrogenation of adsorbed atomic carbon to methane, following the reaction sequence C+4 H?CH+3 H?CH₂+2 H?CH₃+H?CH₄, are studied on Fe(100) by means of density functional theory. An assessment is made on whether the adsorption energies and overall energy profile are affected when zero‐point energy (ZPE) corrections are included. The C, CH and CH₂ species are most stable at the fourfold hollow site, while CH₃ prefers the twofold bridge site. Atomic hydrogen is adsorbed at both the twofold bridge and fourfold hollow sites. Methane is physisorbed on the surface and shows neither orientation nor site preference. It is easily desorbed to the gas phase once formed. The incorporation of ZPE corrections has a very slight, if any, effect on the adsorption energies and does not alter the trends with regards to the most stable adsorption sites. The successive addition of hydrogen to atomic carbon is endothermic up to the addition of the third hydrogen atom resulting in the methyl species, but exothermic in the final hydrogenation step, which leads to methane. The overall methanation reaction is endothermic when starting from atomic carbon and hydrogen on the surface. Zero‐point energy corrections are rarely provided in the literature. Since they are derived from C? H bonds with characteristic vibrations on the order of 2500–3000 cm^?1, the equivalent ZPE of 1/2 hν is on the order of 0.2–0.3 eV and its effect on adsorption energy can in principle be significant. Particularly in reactions between CH_x and H, the ZPE correction is expected to be significant, as additional C? H bonds are formed. In this instance, the methanation reaction energy of +0.77 eV increased to +1.45 eV with the inclusion of ZPE corrections, that is, less favourable. Therefore, it is crucial to include ZPE corrections when reporting reactions involving hydrogen‐containing species.     

Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study

The relative energies of 11 [C₃H₃O]⁺ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3-21G and 4-31G* basis set and configuration interaction). The four most stable structures are: a ([CH₂?CH? CO]⁺), b c ([CH?C? CHOH]⁺) and d ([CH₂?C?COH]⁺); their relative energies at the CI/4-31G*//3-21G level are 0, 117, 171 and 218 kJ mol^?1, respectively. The isomerizations c→[CH?CH? CHO]⁺→[CH₂?C? CHO]⁺→ a and dissociations into [C₂H₃]⁺+CO and [HCO]⁺+C₂H₂ are explored. The calculated potential energy profile reveals that the energy-determining step is the 1,3-H migration c→[CH?CH? CHO]⁺. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.     

Isotope effects and H/D scrambling in the fragmentation of labelled propenes

The fragmentation reaction [C₃(H,D)₆]⁺· → [C₃(H,D)₅]⁺ + (H, D) has been examined in the metastable decomposition region for two pairs of labelled propenes: CH₃CD?CH₂,CD₃CH?CD₂ and CD₃CH?CH₂, CH₃CD?CD₂. The results indicate that complete hydrogen scrambling occurs in the propene molecular ion prior to fragmentation. The isotope effect kH/kD is in the range 2·1 to 3·3.     

Doubly charged benzene and isomeric dications. Fragmentation energetics and charge distributions calculated by MINDO/3 molecular orbital theory

MINDO/3 calculations for singlet and triplet doubly charged benzene [C₆H₆]²⁺ are in satisfactory agreement with the experimentally determined values of the vertical double ionization energy of benzene; calculations for straight chain isomeric structures are consistent with the observed kinetic energy release on fragmentation to [C₅H₃]⁺ and [CH₃]⁺. Symmetrical doubly charged benzene ions relax to a less symmetrical cyclic structure having sufficient internal energy to fragment by ring opening and hydrogen transfer towards the ends of the carbon chain. Fragmentation of [CH₃C₄CH₃]²⁺ to [CH₃C₄]⁺ and [CH₃]⁺ is a relatively high energy process (A), whereas both (B): [CH₃CHC₃CH₂]²⁺ to [CHC₃CH₂]⁺ and [CH₃]⁺ and (C): [CH₃CHCCHCCH]²⁺ to [CHCCHCCH]⁺ and [CH₃]⁺ may be exothermic processes from doubly charged benzene. Furthermore, the calculated energy for the reverse of process (A) is less than the experimentally observed kinetic energy released, whereas larger energies for the reverse of processes B and C are predicted. Heats of formation of homologous series [HC_n]⁺, [CH₃C_n]⁺, [CH₂C_n?2CH]⁺, [CH₃C_n?2CH₂]⁺ and [CH₂?CHC_n?3CH₂]⁺ with 1 < n < 6 are calculated to aid prediction of the most stable products of fragmentation of doubly charged cations. The homologous series [CH₂C_n?2CH]⁺ is relatively stable and may account for ready fragmentation of doubly charged ions to [C_nH₃]⁺; alternatively the symmetrical [C₅H₃]⁺ ion [CHCCHCCH]⁺ may be formed. Dicoordinate carbon chains appear to be important stabilizing features for both cations and dications.     

Gas-phase ion-molecule reactions of the CH3O+ cation

The methoxy cation, CH₃0⁺, formed by collision-induced charge reversal of methoxr anions with a kinetic energy of 8 keY, has been differentiated from the isomenric CH₂OH⁺ ion by performing low kinetic energy ion-molecule reactions In the radiofrequency-only quadrupole of a reverse-geometry double-focusing quadrupole hybrid mass spectrometer. The methoxy cation reacts with CH₃SH, CH₃?CH=CH₂, (CH₃)₂O, and CH₃CH₂Cl by electron transfer, whereas the CH₂OH⁺ ion reacts by proton transfer with these substrates     

Reaction of ionized propene with methanol: Comparison with CH3OH2+ formation from ionized 2-methylpropanol

Methanol exchanges its hydroxyl hydrogen with deuteriums in ionized propene during the formation of protonated methanol. This exchange is attributed to the interconversion [CH₃CH?CH₂^+. HOCH₃?][CH₂ ?CHCH₂ ⁺H₂OCH₃] in single collisions. The exchange in this ion-molecule reaction is analogous to that observed in the formation of protonated methanol from ionized 2-methylpropanol, supporting the intermediacy of ion-neutral complexes in the final step of the latter reaction. Ion-molecule reactions were studied using a Fourier transform mass spectrometer.     

IPr3Si3Cl5+: A Highly Reactive Cation with Silanide Character

The reaction of a metastable SiCl₂ solution with the sterically less‐demanding carbene N,N‐diisopropylimidazo‐2‐ylidene (IPr) yields the salt [(IPr₃Si₃Cl₅)⁺]Cl^? ( 1 ‐Cl), containing a silyl cation with a Si₃ backbone. Salt 1 is highly reactive, but it can be used as a reagent in deuterated dichloromethane, whereby dehalogenation with Me₃SiOTf (OTf=O₃SCF₃) gives the dicationic silyl halide [(IPr₃Si₃Cl₄)]²⁺ 2 . Quantum chemical calculations show that the HOMO is localized at the negatively charged central silicon atom of 1 and 2 , and thus although both compounds are cations they are better described as silanides, which was also corroborated by NMR investigations.     

The site of ionization in the acetylation of aliphatic esters by [(CH3CO)3]+

A series of esters RCOOR′ (where R, R′ = CH₃, CH₃CH₂, (CH₃)₂CH, (CH₃)₃C) were reacted with the [(CH₃CO)₃]⁺ ion from biacetyl in an ion cyclotron resonance spectrometer. A steric effect influences the rate of formation of stable products [RCOOR′·CH₃CO]⁺ and is used to determine that either oxygen of the ester may be initially acylated by [(CH₃CO)₃]⁺.