SiH+5 and the proton affinity of monosilane

Tandem mass spectrometric studies show that SiH⁺₅ is formed in bimolecular reactions of SiH₄ and NH⁺₂, C₂H⁺₃, C₂H⁺₆ and C₃H⁺₈ ions. The dependence of the reaction cross sections on ion energy indicates the formation of SiH⁺₅ from NH⁺₂, C₂H⁺₃, and C₂H⁺₆ to be exothermic reactions, while formation from C₃H⁺₈ is endothermic. Using known thermochemical data, these facts permit the assignment of 150 and 156 kcal/mole to the lower and upper limits of the proton affinity of monosilane.     

Mass spectrometry of π-complexes of transition metals : X. Methylferrocene

The study of deuterium labelled methylferrocenes has shown the ions C₁₁H₁₁Fe⁺, C₆H₆Fe⁺, C₅H₆Fe⁺ to originate from the isomerised form of the molecular ion in which all the hydrogen atoms are redistributed among the ligands.     

Reactivity of Diarylnitrenium Ions

Hydride abstraction from diarylamines with the trityl ion is explored in an attempt to generate a stable diarylnitrenium ion, Ar₂N⁺. Sequential H-atom abstraction reactions ensue. The first H-atom abstraction leads to intensely colored aminium radical cations, Ar₂NH^.+, some of which are quite stable. However, most undergo a second H-atom abstraction leading to ammonium ions, Ar₂NH₂⁺. In the absence of a ready source of H-atoms, a unique self-abstraction reaction occurs when Ar=Me₅C₆, leading to a novel iminium radical cation, Ar=N^.+Ar, which decays via a second self H-atom abstraction reaction to give a stable iminium ion, Ar=N⁺HAr. These products differ substantially from those derived via photochemically produced diarylnitrenium ions.     

Elucidating the structures of isomeric silylenium ions (SiC3H 9 + , SiC4H 11 + , SiC5H 13 + ) by using specific ion/molecule reactions

Specific ion/molecule reactions are demonstrated that distinguish the structures of the following isomeric organosilylenium ions: Si(CH₃) ₃ ⁺ and SiH(CH₃)(C₂H₅)⁺; Si(CH₃)₂(C₂H₅)⁺ and SiH(C₂H₅) ₂ ⁺ ; and Si(CH₃)₂(i?C₃H₇)⁺, Si(CH₃)₂(n?C₃H₇)⁺, Si(CH₃)(C₂H₅) ₂ ⁺ , and Si(CH₃)₃(π?C₂H₄)⁺. Both methanol and isotopically labeled ethene yield structure-specific reactions with these ions. Methanol reacts with alkylsilylenium ions by competitive elimination of a corresponding alkane or dehydrogenation and yields a methoxysilylenium ion. Isotopically labeled ethene reacts specifically with alkylsilylenium ions containing a two-carbon or larger alkyl substituent by displacement of the corresponding olefin and yields an ethylsilylenium ion. Methanol reactions were found to be efficient for all systems, whereas isotopically labeled ethene reaction efficiencies were quite variable, with dialkylsilylenium ions reacting rapidly and trialkylsilylenium ions reacting much more slowly. Mechanisms for these reactions and differences in the kinetics are discussed.     

Fragmentation of ion–molecule adducts of transition metal ions with aromatic ring-containing nitriles in the gas phase

Gas-phase ion–molecule reactions of transition metal ions, M⁺ (M⁺ = Ni⁺, Co⁺, Fe⁺ and Mn⁺), with six aromatic ring-containing nitriles were investigated in a modified fast atom bombardment (FAB) source. It is shown that the monoadduct, (Ph(CH₂)_nCN)–M⁺, is one of the most abundant ion–molecule reaction products. The main fragments in the FAB source are the [C₇H₇]⁺ and [C₈H₉]⁺ ions, and their formation is shown to involve metal ion insertion into the nitriles rather than direct bond cleavage from the ‘free’ or complexed nitriles after FAB ionization. An intramolecular oxidation–reduction reaction, giving [C₇H₇]⁺, is found in the metastable and collisionally induced dissociations of benzyl nitrile adducts accompanied by neutral MCN formation, but not seen for longer chain samples. An ortho effect is observed in the elimination of HCN from the 2-methylbenzyl nitrile adduct ions. This reaction dominates the metastable ion spectrum of the adduct of Mn⁺, whereas metal detachment is nearly the major process for the other complexes of Mn⁺. The different bond-insertion selectivities of the metal ions are also shown.     

Theoretical and Experimental Study of Complex Ions from Reactions of Al+ (Cu+) with Amine Molecules

The gas phase reactions of metal ions (Al⁺, Cu⁺) with amine molecules [CH₃NH₂=MA, (CH₃)₂NH=DMA] were investigated using a laser ablation‐molecular beam method. The directly associated product complex ions,Al⁺‐MA and Al⁺‐DMA, and the dehydrogenation product ions, Cu⁺(CH₂NH) and Cu⁺(C₂H₅N), as well as hydrated ion Cu⁺(NC₂H₅·H₂O), have been obtained and recorded from the reactions of the metal ions and organic amine molecules, and density functional theory (B3LYP) calculations have been performed to reveal the optimized geometry, energetics, and reaction mechanism of the title reactions with basis set 6‐311+G(d,p) adopted.     

Electrophilic aromatic substitution under chemical ionization conditions. Methylamine and ammonia as reagent gases

For compounds C₆H₅X (X?Cl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH₂CH₃]⁺ and by [NH₂]⁺˙. C₆H₅F is less reactive; it gives some [C₆H₅NH₂]⁺˙. Nitrobenzene gives an adduct ion [M+CH₃NH₃]⁺, a reduction product ion [C₆H₅NO₂]⁺˙, and an ion at m/z93, probably a substitution product [C₆H₅NH₂]⁺˙, but no [C₆H₅NH₂CH₃]⁺. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C₆H₅. CO. X give adduct ions and some substitution, mainly [C₆H₅NH₂]⁺˙.     

Propane activation by MC5H5 (M = Ni and Co): An experimental and theoretical work

The reactions of MC₅H⁺₅ (M = Ni and Co) with propane in gaseous phase have been studied with an ion trap mass spectrometer; the MC₅H⁺₅ ions are able to activate the propane molecule which undergoes a dehydrogenation reaction. At variance with the reactions of the bare metal ions no loss of methane is observed; the reaction mechanism has been explored by means of DFT calculations and a possible explanation is offered for the different reactivity of these ligated ions.     

Ion cyclotron resonance studies of some reactions of C+ ions

Product distributions and rate constants for the reaction of ground state C⁺ ions with O₂, NO, HCl, CO₂, H₂S, H₂O, HCN, NH₃, CH₄, H₂CO, CH₃OH, and CH₃NH₂ have been measured. Rate constants were obtained using ion cyclotron resonance trapped ion methods at JPL, and product distributions were obtained using a tandem (Dempster-ICR) mass spectrometer at the University of Utah. Rapid carbon isotope exchange has also been observed in C⁺-CO collisions.     

Reaction of ammonia with accelerated benzoyl ions under multiple-collison conditions in a triple quadrupole instrument

The reaction of benzoyl ion with ammonia in multiple-collision conditions in the second quadrupole assembly of a triple quadrupole mass spectrometer at (laboratory) ion kinetic energies from 0 to 20 eV produced the even-electron ions [C₆H₅]⁺, [C₆H₅NH₃·(NH₃)_m]⁺ (m = 0, 1) and [C₆H₅CONH₃·(NH₃)_n]⁺ (n = 0, 1, 2, 3) and the odd-electron ions [C₆H₄NH₃·(NH₃)_p]⁺· (p = 0, 1). Thermochemical information could not be obtained under multiple-collision conditions: both exothermic and endothermic reactions were observed, with no translational-energy onset measurable for the endothermic processes, nor decrease in the yield of the exothermic processes at high energies. The behaviour of cluster-ion intensities as pressure varied was qualitatively as expected. There are pressure and energy regions where spectra change little; if this feature were to be general, it would point to some utility for these conditions in qualitative analysis.     

Transition-metal mediated heteroatom removal by reactions of FeL+ [L=O,C4H6, c-C5H6, c-C5H5, C6H6, C5H4(=CH2)] with furan,thiophene, and pyrrole in the gas phase

Reactions of Fe⁺ and FeL⁺ [L=O, C₄H₆, c-C₅H₆, C₅H₅, C₆H₆, C₅H₄(=CH₂)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe⁺, Fe(C₅H₅)⁺, and FeC₆H ₆ ⁺ yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺], as well as FeC₅H₄(=CH₂)⁺ and FeO⁺, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC₄H₆ ⁺, Fe(c-C₅H₆)⁺, and FeC₅H₄(=CH₂)⁺. In addition, FeC₄H ₆ ⁺ and Fe(c-C₅H₆)⁺ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C₅H₆)⁺ with pyrrole and thiophene is hydrogen-atom displacement, which implies D^O(Fa(N₅H₅)⁺-C₄H₄X)>D^O(Fe(C₅H₅)⁺-H)=46±5 kcal mol^?1. D^O(Fe⁺-C₄H₄S) and D^O(Fe⁺-C₄H₅N)=D^O(Fe⁺-C₄H₆)=48±5 kcal mol^?1. Finally, 55±5 kcal mol^?1=D^O(Fe⁺-C₆H₆)>D^O(Fe⁺-C₄H₄O)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mol^?1. FeO⁺ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D^O(Fe⁺-CS)>D^O(Fe⁺-C₄H₄S)≈48±5 kcal mol^?1 and D^O(Fe⁺-C₄H₅N)≈48±5 kcal mol^?1>D^O(Fe⁺-HCN)>D^O(Fe⁺-C₂H₄)=39.9±1.4 kcal mil^?1.     

A mass spectral study of 1-(aryldimethylsilyl)-2-propanones and their isomeric 2-(aryldimethylsiloxy)-1-propenes

The mass spectra of a series of β-ketosilanes, p-Y? C₆H₄Me₂SiCH₂C(O)Me and their isomeric silyl enol ethers, p-Y? C₆H₄Me₂SiOC(CH₃)?CH₂, where Y = H, Me, MeO, Cl, F and CF₃, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]⁺, [M? C₆H₄Y·]⁺, [M? Me₂SiO]⁺˙, [M? C₃H₄]⁺˙, [M? HC?CCF₃]⁺˙, [Me₂SiOH]⁺˙ and [C₃H₆O]⁺˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me₂SiO]⁺˙ and [Me₂SiOH]⁺˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.     

The formation of the anilinium ion from the ammonium ion in the ammonia chemical ionization of substituted benzenes

Compounds C₆H₅X(X ? F, Cl, Br, NO₂, CN, OCH₃) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C₆H₅NH₃]⁺ (m/z 94). [NH₄]⁺ reacts with C₆H₅X(X ? F, Cl, Br) to yield m/z 94 but C₆H₅X (X ? CN, NO₂) forms this ion only by reactions involving either [NH₃]⁺ or [C₆H₅X]⁺. C₆H₅OCH₃ does not form m/z 94.     

Chemical ionization mass spectra of alkylphenol and linear alcohol polyethoxylates

The chemical ionization mass spectra of some tert-octylphenol ethoxylates and linear alcohol ethoxylates have been determined using methane and ammonia as reactant gases. Proton, [C₂H₅]⁺ and [C₃H₅]⁺ adducts were observed with attachment on the ring as well as on the oxyethylene chain for the tertiary octylphenol ethoxylates. Proton and [NH₄]⁺ addition reactions were also observed. Alkyl ion and olefin displacement reactions were also important fragmentations. Hydride abstraction and proton, [C₂H₅]⁺, [C₃H₅]⁺ and [NH₄]⁺ attachment were the most important reactions occurring for the linear alcohol ethoxylates.     

Rearrangements and fragmentations of [C2H5S]+ ions

[C₂H₅S]⁺ ions (m/e 61) with different initial structures were generated in the mass spectrometer from twelve precursor ions. Abundance ratios of competing metastable ion decompositions were used to determine whether these ions decompose through the same or different reaction channels. It was concluded that all [C₂H₅S]⁺ ions isomerize to a common structure or mixture of structures prior to decomposition in the first field free region. From ¹³C labelling experiments it was concluded that [C₂H₅S]⁺ ions generated from the molecular ions of 2-propanethiol-2-[¹³C], partially rearrange to a symmetrical structure before decomposition to [CHS]⁺ and CH₄, whereas in [C₂H₅S]⁺ ions generated from the the molecular ions of 1,2-bis-(thiomethoxy-[¹³C]) ethane, the two carbon atoms become fully equivalent before CH₄ loss occurs.     

Reactive Half‐Metallocenium Ionic Liquids That Undergo Solventless Ligand Exchange

The piano‐stool half‐metallocenium cations [Fe(C₅R₅)(CO)₂ L ]⁺ (C₅R₅=C₅H₅, C₅Me₅, C₅Me₄Et; L =1‐pentene, nBuCN, MeCN, Me₂S, NH₃, NMe₃, pyridine) provide ionic liquids (ILs) with the bis(trifluoromethanesulfonyl)imide (Tf₂N) anion without introducing long alkyl chains. Their melting points are affected by molecular symmetry, and their thermal stabilities reflect the strength of the metal–ligand bonding. These are reactive liquids that show solventless ligand exchange reactions by gas absorption. The direction of the ligand‐exchange reaction is correlated with the stabilities. Based on the variation of the melting points, these ILs undergo transformations between the liquid and solid phases associated with the reaction.     

A tandem mass spectrometry study of the gas phase RSC6H5Cr+L (R = H,C6H5; L = arene) and C6H5SSC6H5Cr+ ions

Ion-molecule reactions of chromium containing ions with arylsulfides have been studied in the gas phase and their products have been characterized by tandem mass spectrometry. C₆H₅SH and (C₆H₅)₂S react as typical aromatic compounds and give rise to Cr⁺C₆H₅SR] and RC₆H₅Cr⁺QH₅SR′ [R = H, CH₃, CH(CH₃)₂; R′ = H, C₆H₅] ions. Metastable ion mass spectra of the latter species show that the metal is more strongly bound to diphenylsulfide than to alkylbenzenes. C₆H₅SSC₆H₅ reacts with chromium-containing ions to form only Cr⁺(C₆H₅SSC₆H₅). The decomposition characteristics of this ion and, in particular, the presence of a recovery signal in the neutralization-reionization mass spectrum are in keeping with the formation of a 1,2-dithia[2]cyclophane complex ion, which rearranges into a structurel(s) that contains Cr?S bond(s). No evidence was found for metal atom insertion into S?S, C?S, or S?H bonds.     

Gas-phase reactions between O−. and C6H5F: On the acidity of fluorobenzene and 1,4-difluorobenzene

The gas-phase reactions of negative ions (O^-., NH ₂ ^? , C₂H₅NH^?, (CH₃)₂N^?, C₆H ₅ ^t- , and CH₃SCH ₂ ^? ) with fluorobenzene and 1,4-difluorobenzene have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The O^?. ion reacts predominantly by (1) proton abstraction, (2) formal H ₂ ^+. abstraction, and (3) attack on an unsubstituted carbon atom. In addition to these processes, attack on a fluorine bearing carbon atom yielding F^? and C₆H₄FO^? ions occurs with 1,4-difluorobenzene. Site-specific deuterium labeling reveals the occurrence of competing 1,2-, 1,3-, and 1,4-H ₂ ^+. abstractions in the reaction of O^?. with fluorobenzene. Attack of the O^?. ion on the 3- and 4-positions in fluorobenzene with formation of the 3- and 4-fluorophenoxide ions, respectively, is preferred to reaction at the 2-position, as indicated by the relative extent of loss of a hydrogen and a deuterium atom in the reactions with labeled fluorobenzenes. The NH ₂ ^? , C₂H₅NH^?, (CH₃)₂N^?, C₆H ₅ ^? , and CH₃SCH ₂ ^? anions react with fluoroberuene and 1,4-difluorobenzene only by proton abstraction. The relative importance of H⁺ and D⁺ abstraction in the reaction of these anions with labeled fluorobenzenes indicates that the 2-position in fluorobenzene is more acidic than the 3- and 4-positions, suggesting that the literature value of the gas-phase acidity of this compound (ΔH _acid ^o = 1620 ± 8 kJ mol^?1) refers to the former site. Based on the occurrence of reversible proton transfer between the CH₃O^? ion and 1,4-difluorobenzene, the ΔH _acid ^o of this compound is redetermined to be 1592 ± 8 kJ mol^?1.     

FTMS studies of sputtered metal cluster ions (IV): size-selective effects in the chemistry of Fe n + with NH3 and Pd n + with D2 or C2H4

Fe _n ⁺ and Pd _n ⁺ clusters up ton=19 andn=25, respectively, are produced in an external ion source by sputtering of the respective metal foils with Xe⁺ primary ions at 20 keV. They are transferred to the ICR cell of a home-built Fourier transform mass spectrometer, where they are thermalized to nearly room temperature and stored for several tens of seconds. During this time, their reactions with a gas leaked in at low level are studied. Thus in the presence of ammonia, most Fe _n ⁺ clusters react by simply adsorbing intact NH₃ molecules. Only Fe ₄ ⁺ ions show dehydrogenation/adsorption to Fe₄(NH) _m ⁺ intermediates (m=1, 2) that in a complex scheme go on adsorbing complete NH₃ units. To clarify the reaction scheme, one has to isolate each species in the ion cell, which often requires the ejection of ions very close in mass. This led to the development of a special isolation technique that avoids the use of isotopically pure metal samples. Pd _n ⁺ cluster ions (n=2...9) dehydrogenate C₂H₄ in general to yield Pd _n (C₂H₂)⁺, yet Pd ₆ ⁺ appear totally unreactive. Towards D₂, Pd ₇ ⁺ ions seem inert, whereas Pd ₈ ⁺ adsorb up to two molecules.     

Deposition of Diamondlike Carbon Film and Mass Spectrometry Measurement in CH4/N2 RF Plasma

The deposition of diamondlike carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH₄/N₂ RF (13.56 MHz) plasma at 0.1 Torr. The film deposition rate greatly depended on both CH₄/N₂ composition ratio and RF power input. It was decreased monotonically as CH₄ content decreased in the plasma and then rapidly diminished to negligible amounts at a critical CH₄ content, which became large for higher RF power. The rate increased with increasing RF power, reaching a maximum value in 40% CH₄ plasma. The predominant ionic products in CH₄/N₂ plasma were NH⁺ ₄ and CH₄N⁺ ions, which were produced by reactions of hydrocarbon ions, such as CH⁺ ₃, CH⁺ ₂, CH⁺ ₅, and C₂H⁺ ₅ with NH₃ molecules in the plasma. It was speculated that the production of NH⁺ ₄ ion induced the decrease of C₂H⁺ ₅ ion density in the plasma, which caused a reduction in higher hydrocarbon ions densities and, accordingly, in film deposition rate. The N⁺ ₂ ion sputtering also plays a major role in a reduction of film deposition rate for relatively large RF powers. The incorporation of nitrogen atoms into the bonding network of the DLC film deposited was greatly suppressed at present gas pressure conditions.