Cyclotron Resonance Study Research Articles

A fourier transform-ion cyclotron resonance study of steric effects on proton transfer reactions of polyalkyl benzenes

The rates of deprotonation, MH + + B → M + BH + (M = 1, 2), and the rates of protonation, M + BH + → MH + + B (M = 2, 3, 4), have been measured by Fourier transform-ion cyclotron resonance (FT-ICR) spectrometry for the increasingly sterically crowded alkyl benzenes ethylbenzene, 1; 1,3,5-trimethylbenzene (mesitylene), 2; 3,5-di( t-butyl)toluene, 3; 1,3,5-tri( t-butyl) benzene, 4; and a series of n-bases B. In addition, the gas phase basicities of 3 and 4 were determined by proton transfer equilibrium measurements using FT-ICR. The efficiencies of deprotonation and protonation are always large (> 50%) for exoergic reactions and increase with increasing exoergicity, but never reach unit efficiency. For each of the alkylated benzenes 1– 4 the efficiency decreases steeply at the border between exoergic and endoergic reactions. This is the “normal” behaviour of proton transfer reactions and shows the absence of steric effects for proton transfer to and from alkylated benzenes even in the case of 3 and 4 substituted by bulky t-butyl groups, and is in complete contrast to the behaviour of t-butylated pyridines. This difference is explained by different geometries of the transition state for the proton transfer reactions in the case of the alkylated pyridines and alkylated benzenes, and by the critical role of π-complexes in proton transfer reactions of benzene derivatives.

A fourier transform‐ion cyclotron resonance study of the reactivity of ionized vinylalcohol with selected unsaturated compounds

AbstractReactions between CX2CXOX+· (X  H or D) and alkenes, an alkyne, benzene, aldehydes and ketones have been studied by Fourier transform mass spectrometry. Most of the neutral species undergo charge exchange or proton transfer reactions with high rates; l‐alkenes lead to slower cycloaddition reactions. The thermochemistry and considerations on the reaction specificities are discussed.

Quadrupole-detection FT-ICR mass spectrometry

A new detection scheme for Fourier transform-ion cyclotron resonance (FT-ICR) studies is proposed and initial experimental results are presented. While in conventional FT-ICR the difference of the transient signals from two opposite electrodes yields a signal at the reduced cyclotron frequency v +, which depends on the applied trapping voltage and space charge, it is also possible to use the difference of the sum of these signals and the sum of a similar set of electrodes perpendicular to the first. In this way resonances are observed at the harmonic of the reduced cyclotron frequency, 2· ν +, as well as at ( v + + v -). The latter is interesting in respect of accurate mass measurements, since ( v + + v -) does not depend on the trapping voltage.

Differentiation of diastereoisomeric terpenoid alcohols by electron impact and negative ion chemical ionization associated with collision‐induced dissociation. A fourier transform ion cyclotron resonance study

AbstractElectron impact ionization‐collision‐induced dissociation (EI‐CID) and negative ion chemical ionization‐collision‐induced dissociation (NICI‐CID) experiments have been performed on the molecular or quasi‐molecular ions (M+· or [M ‐ H]−) of series of terpenoid alcohols, using a Fourier transform ion cyclotron resonance spectrometer. These terpenes belong to the p‐menthane family and bear a hydroxyl group in various positions relative to the isopropyl or isopropenyl substituent (positional or stereochemical isomers). In the case of positional isomers, different CID spectra were always obtained. Within a given diastereoisomeric series, stereochemical differences were also observed in both NICI‐CID and EI‐CID experiments.

ChemInform Abstract: Mechanism of CH·+ 2 Transfer from Distonic Ions X-CH·+ 2 (X: CH2O, CH2CH2) to π- and n-Electron Bases in the Gas Phase. A Fourier Transform Ion Cyclotron Resonance (FTICR) Study Supplemented by ab initio MO Calculations.

ChemInform Abstract: Mechanism of CH·+ 2 Transfer from Distonic Ions X-CH·+ 2 (X: CH2O, CH2CH2) to π- and n-Electron Bases in the Gas Phase. A Fourier Transform Ion Cyclotron Resonance (FTICR) Study Supplemented by ab initio MO Calculations.

Bound state cyclotron resonance in modulation doped GaAs-Al xGa 1−xAs quantum wells

We report studies of the far-infrared cyclotron resonance in two GaAs-Al x Ga 1− x As quantum well samples. The resonance positions are always shifted to considerably higher energies than would be expected for free carriers, and are best described by the relation (ħω) 2 = (ħω c) 2 + Δ 2 where ω c is the free carrier cyclotron frequency and Δ is a binding energy due to a locally harmonic potential. Two distinct offsets can be observed, with a larger offset at higher field and a region of transition between them. The transition region is centered on ν = 2, and the magnitude of the high field offset decreases with increasing electron concentration.

Unusual positive ion reagents in chemical ionization mass spectrometry

This review covers the literature up to 1988, and emphasis is given to the analytical applications of the special reagents. Many of the reagents discussed in the present article have strong fundamental basis from ion cyclotron resonance (ICR) studies, but these aspects have not been included in this survey

Fourier transform ion cyclotron resonance study of the gas‐phase reaction of the yttrium ion with silane

AbstractPreliminary results obtained with a home‐made Fourier transform ion cyclotron resonance mass spectrometer on the sequential clustering reactions of silane using yttrium cation activation are reported. [YSinH2n]+ and [YSinH2n − 2]+ ions are formed. So far, we have observed these ions up to n = 7, and a sequential clustering mechanism is proposed. The ion structures are characterized by collision‐induced dissociation, and kinetic measurements to determine the formation and decay rates of each ion are performed.

A new detection scheme for Fourier transform-ion cyclotron resonance spectrometry in Penning traps

A new detection scheme for Fourier transform-ion cyclotron resonance (FT-ICR) studies is proposed and initial experimental results are presented. While in conventional FT-ICR, the difference of the transient signals from two opposite electrodes is recorded and Fourier transformed, it is also possible to use the sum of these signals. In this way resonances are observed at the harmonic of the reduced cyclotron frequency 2 ν+ as well as ν+−ν− and ν++ν−, the later being important for accurate mass measurements. The experiments were performed with a Penning trap in an electromagnet.

Fourier transform ion cyclotron resonance studies of sputtered metal cluster ions: The chemistry of Cu n+ with O 2

In a new apparatus, combining an external sputtering ion source with an ion storage cell, we have studied the chemical reactions of mass-selected copper cluster cations with oxygen. Trapped and thermalized, they show no tendency to react, but when additionally excited they undergo low-energy collision-induced dissociation. Different parent ions fragment in a similar pattern, with Cu 5O 2 + and Cu 3O + as common reaction products that display extraordinary stability, in analogy to the well known hydrated protons H 2 n+1 O n +. The oxygen does not simply adsorb to the original Cu n + cluster, but causes its complete restructuring

Ion molecule reactions in di-isopropyl ether

The reactions of the ions at m/ z 43 and m/ z 45 which are formed by direct electron ionization of di-isopropyl ether with the parent molecules to produce ions at m/ z 61 may be examples of fast endothermic reactions. High pressure mass spectrometric studies indicated rapid reactions of these fragment ions with no significant temperature coefficients. Precise mass measurements and collisionally-induced decomposition studies indicate that the ion at m/ z 61 in di-isopropyl ether is a protonated alcohol. Trapped ion Fourier transform—ion cyclotron resonance studies gave rate constants for these reactions which were almost the same as the theoretical collision rate constants. Trapped ion studies in a Fourier transform—ion cyclotron resonance showed no significant radiative or collisional deactivation of the ions at m/ z 45 on the time scale of seconds, an observation which suggests that the reaction is not that of excited ions.

Heating and confinement studies of electron cyclotron resonance heated plasmas in Heliotron E

Radiofrequency (RF) heating of currentless plasmas is performed at the fundamental electron cyclotron frequency. The absorbed power profile is determined from the decay of the electron internal energy profile immediately after the RF pulse is turned off. Measurements of the absorbed power profile at various positions of the cyclotron resonance layer are compared with single-pass absorption profiles predicted by a ray tracing code. The profiles of electron temperature, density and ion temperature are studied as a function of the absorbed power, its radial profile and the electron line averaged density. Finally, a scaling of the energy confinement time obtained by regression analysis is compared with a scaling for neutral beam heated plasmas.

A gas‐phase anionic analog of the wittig reaction. An ion cyclotron resonance study of the gas‐phase ion chemistry of silyl carbanions

AbstractGas‐phase ion–molecule reactions of a variety of fluorosilyl carbanions with compounds containing double bonds to oxygen, XO, have been examined using pulsed ion cyclotron resonance spectroscopy. The predominant reaction channel observed for species not containing acidic hydrogens is a Wittig‐like process involving SiO bond formation and elimination of XCH2 species. The gas‐phase acidity of F3Si(CH3) has been determined and those of F2Si(CH3)2 and FSi(CH3)3 have been estimated. From the fluoride transfer reactions of F3SiCH2− the fluoride affinity of F2SiCH2 has been estimated and limits on the π bond strength in this silaethene obtained. Potential analytical applications of the Wittig reactivity have been discussed.

Gas‐phase ion–molecule reactions of thioic and dithioic acid derivatives. Condensation reactions with alkenes and alkynes

AbstractA Fourier transform–ion cyclotron resonance study of thioacyl compounds as binary mixtures with unsaturated hydrocarbons has revealed that thioacetylium ions CH3CS+ generated by electron fragmentation fail to thioacyl‐ate even the most reactive aromatic hydrocarbons. Among the hydrocarbons studied, only 3‐hexyne and 2,4‐dimethyl‐2,5‐hexadiene were observed to react with CH3CS+. Apart from proton‐transfer reactions, the major ionic reaction of thioesters with arenes, alkynes and alkenes is condensation of the molecular ion of one component, usually the ester, with a neutral molecule of the other, resulting in the cleavage of the SCalkyl bond of the thioester. The nature of this reaction is discussed and a possible mechanism is suggested.

Cyclotron-resonance studies of electronic properties in ZnSe.

Cyclotron-resonance studies of electronic properties in ZnSe.

Photoluminescence and cyclotron resonance studies on highly purified ZnSe single crystals

We have prepared high purity ZnSe single crystals with donor concentrations less than 1015/cm3 and characterized the doped and undoped ZnSe single crystals using photoluminescence and cyclotron resonance techniques. Photoluminescence and photoluminescence excitation spectra on the purest crystal reveal (1) that a Zn-dip treatment increases the free exciton life time, (2) that the free excitons recombine on the lower excitonic polariton branch, (3) that the intensities of I3 become larger than those of I2, and (4) that each I3 line has excited states, which are rather more complicated than those of the I2 lines. We have observed for the first time cyclotron resonance absorption of photoexcited electrons and holes. This means that the grown crystals are not only of high purity but also of high quality. Isotropic effective masses (m∗e = 0.145m0 and m∗h = 1.04m0) and cyclotron mobilities at 4.2 K (μe = 470,000 cm2/V·s and μh = 210,000 cm2/V·s) have been obtained. Doping experiments with In and Cu reveal that the difficulties of preparing low resistivity p-type crystals, such as self-compensation and the amphoteric behavior of dopants, can be solved by heat treatments after doping.

Fourier transform mass spectrometric studies of Al +, Ga + and In + with organic neutral molecules and alkyl halides

Gas-phase ion/molecule reactions of Al +, Ga +, and In + with alcohols, ketones, esters, and alkyl halides are studied using laser desorption-Fourier transform mass spectrometry (LD-FTMS). Chloride, bromide, and hydroxide affinities are reported, as are the primary and secondary reaction products. Present results are compared with previous ion-beam and ion cyclotron resonance studies of Al + and found to be in good agreement. The potential of the metal ions studies as possible selective chemical ionization reagents is discussed.

Cyclotron-resonance study of nonparabolicity and screening in GaAs-Ga1-xAlxAs heterojunctions.

Cyclotron-resonance study of nonparabolicity and screening in GaAs-Ga1-xAlxAs heterojunctions.

Nucleophilic substitution in the gas phase. The reactions of alkoxide-alkanol negative ions with boron, carbon, silicon, and titanium alkoxides. An ion cyclotron resonance and ab initio study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNucleophilic substitution in the gas phase. The reactions of alkoxide-alkanol negative ions with boron, carbon, silicon, and titanium alkoxides. An ion cyclotron resonance and ab initio studyHans Van der Wel, Nico M. M. Nibbering, John C. Sheldon, Roger N. Hayes, and John H. BowieCite this: J. Am. Chem. Soc. 1987, 109, 19, 5823–5828Publication Date (Print):September 1, 1987Publication History Published online1 May 2002Published inissue 1 September 1987https://doi.org/10.1021/ja00253a039RIGHTS & PERMISSIONSArticle Views93Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (722 KB) Get e-Alerts Get e-Alerts

A fourier transform ion cyclotron resonance study of the reactions of O −· with methyl formate

It is shown that the different product ion distribution from reactions of O −· with methyl formate as reported in an earlier drift cell ICR and recent FT-ICR study is most probably due to a translational energy effect of the O −· ion. Two new pathways in addition to the previously reported B AC2 and S N2 mechanisms for formation of the formate anion have been found on the basis of deuterium-, 18O- and 13C-labelling experiments.