Cyclotron Resonance Techniques Research Articles

First application of the phase-imaging ion-cyclotron resonance technique at TRIGA-Trap

The phase-imaging ion cyclotron resonance technique (PI-ICR) has been implemented at TRIGA-Trap together with a newly built five-pole cylindrical trap. In PI-ICR the total phase of trapped ions is measured by projecting the ion motion onto a position-sensitive delay-line micro-channel plate detector. The systematic uncertainties have been investigated and first mass measurements on stable Pb isotopes have been performed with PI-ICR. The new technique offers higher mass-resolving power, allows checking for the presence of contaminant ion species, and it proved useful in tuning the harmonicity of the trapping potential as well as in aligning the trap symmetry axis with respect to the magnetic field axis by visualizing the radial ion motion. This is a non-scanning technique where every detected ion contributes equally, therefore it is more sensitive than the previously used time-of-flight ion-cyclotron-resonance (ToF-ICR) technique, which is based on the scanning of the sideband-frequency of trapped ions and recording their time of flight after ejection. It will enable us to carry out high-precision mass measurements in the actinide region with uncertainties on the ppb level.

Multi-CRAFTI: Relative Collision Cross Sections from Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Line Width Measurements.

Determination of collision cross sections (CCS) using the cross-sectional areas by the Fourier transform ion cyclotron resonance (CRAFTI) technique is limited by the requirement that accurate pressures in the trapping cell of the mass spectrometer must be known. Experiments must also be performed in the energetic hard-sphere regime such that ions decohere after single collisions with neutrals; this limits application to ions that are not much more massive than the neutrals. To mitigate these problems, we have resonantly excited two (or more) ions of different m/z to the same center-of-mass kinetic energy in a single experiment, subjecting them to identical neutral pressures. We term this approach "multi-CRAFTI". This facilitates measurement of relative CCS without requiring knowledge of the pressure and enables determination of absolute CCS using internal standards. Experiments with tetraalkylammonium ions yield CCS in reasonable agreement with the one-ion-at-a-time CRAFTI approach and with ion mobility spectrometry (IMS) when differences in collision energetics are taken into account (multi-CRAFTI generally yields smaller CCS than does IMS due to the higher collision energies employed in multi-CRAFTI). Comparison of multi-CRAFTI and IMS results with CCS calculated from structures computed at the M06-2X/6-31+G* level of theory using projection approximation or trajectory method values, respectively, indicates that the computed structures have CCS increasingly smaller than the experimental CCS as m/z increases, implying the computational model overestimates interactions between the alkyl arms. For ions that undergo similar collisional decoherence processes, relative CCS reach constant values at lower collision energies than do absolute CCS values, suggesting a means of increasing the accessible upper m/z limit by employing multi-CRAFTI.

Halide Size-Selective Binding by Cucurbit[5]uril-Alkali Cation Complexes in the Gas Phase.

We report data that suggest complexes with alkali cations capping the portals of cucurbit[5]uril (CB[5]) bind halide anions size-selectively as observed in the gas phase: Cl- binds inside the CB[5] cavity, Br- is observed both inside and outside, and I- binds weakly outside. This is reflected in sustained off-resonance irradiation collision-induced dissociation (SORI-CID) experiments: all detected Cl- complexes dissociate at higher energies, and Br- complexes exhibit unusual bimodal dissociation behavior, with part of the ion population dissociating at very low energies and the remainder dissociating at significantly higher energies comparable to those observed for Cl-. Decoherence cross sections measured in SF6 using cross-sectional areas by Fourier transform ion cyclotron resonance techniques for [CB[5] + M2X]+ (M = Na, X = Cl or Br) are comparable to or less than that of [CB[5] + Na]+ over a wide energy range, suggesting that Cl- or Br- in these complexes are bound inside the CB[5] cavity. In contrast, [CB[5] + K2Br]+ has a cross section measured about 20% larger than that of [CB[5] + Na]+, suggesting external binding that may correspond with the weakly bound component seen in SORI. While I- complexes with alkali cation caps were not observed, alkaline earth iodides with CB[5] yielded complexes with cross sections 5-10% larger than that of [CB[5] + Na]+, suggesting externally bound iodide. Geometry optimization at the M06-2X/6-31+G* level of ab initio theory suggests that internal anion binding is energetically favored by approximately 50-200 kJ mol-1 over external binding; thus, the externally bound complexes observed experimentally must be due to large energetic barriers hindering the passing of large anions through the CB[5] portal, preventing access to the interior. Calculation of the barriers to anion egress using MMFF//M06-2X/6-31+G* theory supports this idea and suggests that the size-selective binding we observe is due to anion size-dependent differences in the barriers.

Three beta-decaying states in 128In and 130In resolved for the first time using Penning-trap techniques

Isomeric states in 128In and 130In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing state-of-the-art ion manipulation techniques, three different beta-decaying states in 128In and 130In have been separated and their masses measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the 15− isomer in 128Sn has been discovered in 128In at 1797.6(20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16+ spin-trap isomer. In 130In, the lowest-lying (10−) isomeric state at 58.6(82) keV was resolved for the first time using the phase-imaging ion cyclotron resonance technique. The energy difference between the 10− and 1− states in 130In, stemming from parallel/antiparallel coupling of (π0g9/2−1)⊗(ν0h11/2−1), has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies of the excited states determined in this work is crucial for producing new improved effective interactions for the nuclear shell model description of nuclei near 132Sn.

SIPT - An ultrasensitive mass spectrometer for rare isotopes

Nuclear structure and astrophysics studies rely heavily on precision mass measurements of rare isotopes. However, many of these isotopes far from the valley of stability can only be produced at very low rates, which are incompatible with the destructive measurement techniques used by rare isotope Penning trap mass spectrometry facilities. To this end, the Low Energy Beam and Ion Trap facility at the National Superconducting Laboratory is in the process of commissioning a single ion Penning trap (SIPT) mass spectrometer that relies on the non-destructive narrowband Fourier Transform ion cyclotron resonance technique. SIPT is the first Penning trap designed to perform mass measurements of rare isotopes produced via projectile fragmentation at rates on the order of one ion per day. The system details and cryogenic detection design, as well as results from the room and cryogenic temperature commissioning, are discussed at length.

High-precision measurement of the mass difference between 102Pd and 102Ru

The Q-value for the neutrinoless double electron capture on 102Pd, Qϵϵ(102Pd), is determined as the atomic mass difference between 102Pd and 102Ru. A precise measurement of the Qϵϵ(102Pd) at the SHIPTRAP Penning trap showed a more than 10σ deviation to the adopted Atomic Mass Evaluation (AME) value. The reliability of the SHIPTRAP measurement was challenged because the AME value was based on numerous experiments including β and electron capture decays and very precise (n, γ) data, all agreeing with each other. To solve the discrepancy, the Qϵϵ(102Pd) has now been determined with the JYFLTRAP Penning trap at the IGISOL facility in the Accelerator Laboratory of the University of Jyväskylä. The measurement was performed both with the Time-of-Flight and the Phase-Imaging Ion Cyclotron Resonance techniques. The obtained result, Qϵϵ(102Pd) = 1203.472(45) keV, is eight times more precise and agrees well with the value obtained at SHIPTRAP, Qϵϵ(102Pd) = 1203.27(36) keV, confirming that 102Pd is not a good candidate for a search for neutrinoless double-electron capture.

Phase-Imaging Ion-Cyclotron-Resonance technique at the JYFLTRAP double Penning trap mass spectrometer

The Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique has been commissioned at the JYFLTRAP double Penning trap mass spectrometer. This technique is based on projecting the ion motion in the Penning trap onto a position-sensitive multichannel-plate ion detector. Mass measurements of stable 85 Rb $ ^{+}$ and 87 Rb $ ^{+}$ ions with well-known mass values show that relative uncertainties $ \Delta m/m \leq 7\cdot 10^{-10}$ are possible to reach with the PI-ICR technique at JYFLTRAP. The significant improvement both in resolving power and in precision compared to the conventional Time-of-Flight Ion Cyclotron Resonance technique will enable measurements of close-lying isomeric states and of more exotic isotopes as well as ultra-high precision measurements required, e.g., for neutrino physics. In addition, a new phase-dependent cleaning method based on the differences in the accumulated cyclotron motion phases has been demonstrated with short-lived 127 In $ ^{+}$ and 127m In $ ^{+}$ ions.

Quantitative Collision Cross-Sections from FTICR Linewidth Measurements: Improvements in Theory and Experiment.

Two corrections to the equation used in the cross-sectional areas by Fourier transform ion cyclotron resonance ("CRAFTI") technique are identified. In CRAFTI, ion collision cross-sections are obtained from the pressure-dependent ion linewidths in Fourier transform mass spectra. The effects of these corrections on the accuracy of the cross-sections obtained using the CRAFTI technique are evaluated experimentally using the 20 biogenic amino acids and several crown ether complexes with protonated alkyl monoamines. Good absolute agreement is obtained between the CRAFTI cross-sections and the corresponding cross-sections obtained using both static drift ion mobility spectrometry and computational simulations. These results indicate that the CRAFTI cross-sections obtained using the updated equation presented here are quantitatively descriptive of the size and shape of the gas-phase ions. Cross-sections that differ by less than 3% are measured for the isobaric isomers n-butylamine and tert-butylamine complexed with the crown ethers. This level of precision is similar to what has been achieved previously using traveling wave ion mobility devices. These results indicate that CRAFTI can be used to probe subtle structural differences between ions with approximately the same precision as that achieved in traveling wave ion mobility devices. Graphical Abstract ᅟ.

Collision Cross Sections for 20 Protonated Amino Acids: Fourier Transform Ion Cyclotron Resonance and Ion Mobility Results.

We report relative dephasing cross sections for the 20 biogenic protonated amino acids measured using the cross sectional areas by Fourier transform ion cyclotron resonance (CRAFTI) technique at 1.9 keV in the laboratory reference frame, as well as momentum transfer cross sections for the same ions computed from Boltzmann-weighted structures determined using molecular mechanics. Cross sections generally increase with increasing molecular weight. Cross sections for aliphatic and aromatic protonated amino acids are larger than the average trend, suggesting these side chains do not fold efficiently. Sulfur-containing protonated amino acids have smaller than average cross sections, reflecting the mass of the S atom. Protonated amino acids that can internally hydrogen-bond have smaller than average cross sections, reflecting more extensive folding. The CRAFTI measurements correlate well with results from drift ion mobility (IMS) and traveling wave ion mobility (TWIMS) spectrometric measurements; CRAFTI results correlate with IMS values approximately as well as IMS and TWIMS values from independent measurements correlate with each other. Both CRAFTI and IMS results correlate well with the computed momentum transfer cross sections, suggesting both techniques provide accurate molecular structural information. Absolute values obtained using the various methods differ significantly; in the case of CRAFTI, this may be due to errors in measurements of collision gas pressure, measurement of excitation voltage, and/or dependence of cross sections on kinetic energy. Graphical Abstract ᅟ.

Gas-Phase Nucleophilic Reactivity of Alkoxysilanes

A reatividade em fase gasosa das alcoxissilanas do tipo Me 4-n Si(OEt) n (n = 1-3) foi investigada por ressonância ciclotronica de ions por transformada de Fourier (FT-ICR) com o intuito de se caracterizar os mecanismos de ataque nucleofilico nesses importantes precursores de novos materiais. Nucleofilos como F - , MeO - e EtO - reagem rapidamente e de forma preferencial atacando o atomo de Si, formando a especie pentacoordenada de Si. Esta em seguida sofre processos de eliminacao iniciados, ou por um ion metidio nascente Me - , ou um ion etoxido EtO - , que por sua vez, podem abstrair um proton gerando carbânions ou siloxidos. Carbânions do tipo X(Me)3-nSi(OEt)nCH2 - (X = F, MeO, EtO e n = 1-3) e siloxidos do tipo X(Me)4-nSi(OEt)n-1O - (X = F, MeO, EtO e n = 2-3) podem ser facilmente dissociados por excitacao multifotonica no infravermelho induzida por um laser de CO 2 gerando uma grande variedade de siloxidos simples e silicatos analogos a especies intermediarias encontradas nas primeiras etapas de processos sol-gel. Para as alcoxissilanas que contem mais grupos etoxido, uma reacao competitiva analoga a uma eliminacao E2 e observada, onde o nucleofilo abstrai um hidrogenio β de um grupo etoxila, eliminando etileno. A cinetica, distribuicao relativa de produtos e termoquimica dessas reacoes tambem sao apresentadas para alguns casos especificos. The gas-phase reactivity of the Me 4-n Si(OEt) n (n = 1-3) alkoxysilanes was investigated by Fourier transform ion cyclotron resonance (FT-ICR) technique in order to characterize the fundamental mechanisms associated with nucleophilic attack on these important precursors of new materials. Typical nucleophiles such as F - , MeO - and EtO - react readily and preferentially by attack at the silicon center with formation of a pentacoordinated siliconate that undergoes elimination processes initiated by either a nascent methide ion, Me, or an ethoxide ion, EtO, that can abstract a proton to yield either a carbanion or a siloxide-type anion. Carbanions of the type X(Me) 3-n Si(OEt) n CH 2 - (X = F, MeO, EtO and n = 1-3) and siloxide ion of the type X(Me)4-nSi(OEt)n-1O - (X = F, MeO, EtO and n = 2-3) can be easily dissociated by infrared multiphoton excitation with a CO2 laser to give rise to a large variety of simple siloxide and silicate-type anions that are reminiscent of intermediate species in the early stages of sol-gel processes. For the higher-ethoxy containing substrates, a competing reaction is observed that is analogous to an E2 elimination reaction in which the nucleophile abstracts a β-proton from the ethoxy group leading to elimination of ethylene. The kinetics, relative product distribution and thermochemistry of these reactions are also reported for some specific cases.

The Gas-Phase Alcoholysis of Protonated Homoleptic Alkoxysilanes

Tetra-alkoxysilanes are common and useful reagents in sol-gel processes and understanding their reactivity is important in the design of new materials. The mechanism of gas-phase reactions that mimic alcoholyis of Si(OMe)(4) (usually known as TMOS) under acidic conditions have been studied by Fourier transform ion cyclotron resonance techniques and density functional calculations at the B3LYP/6-311+G(d,p) level. The proton affinity of TMOS has been estimated at 836.4 kJ mol(-1) and protonation of TMOS gives rise to an ionic species that is best represented as trimethoxysilyl cations associated with a methanol molecule. Protonated TMOS undergoes rapid and sequential substitution of the methoxy groups in the gas-phase upon reaction with alcohols. The calculated energy profile of the reaction indicates that the substitution reaction through an S(N)2 type mechanism may be more favorable than frontal attack at silicon. Furthermore, the sequential substitution reactions are promoted by a mechanism that involves proton shuttle from the most favorable protonation site to the oxygen of the departing group mediated by the neutral reagent molecule.

Photoelectron emission from solid Ne tested by impurity adsorption

Electron emission is obtained from a solid Ne sample growing from the gas phase on a low temperature substrate. The surface of the sample is irradiated by the light of an open-source microwave discharge running in the gaseous Ne. A second gas flow of CH4 is simultaneously passed onto the substrate, avoiding the discharge zone. Free electrons ejected into a vacuum chamber during the sample growth are detected by means of the electron cyclotron resonance (ECR) technique. The electron yield is found to decrease with increasing CH4 flow. Fitting curves to the experimental data show that the surface CH4 impurities play the major role in emission quenching. A temperature effect was observed in which a 4.2K sample was much more sensitive to CH4 doping than a 1.6K one. Based on the experimental results, a model is proposed for the surface sites where electrons escape the solid.

Recent developments in ion detection techniques for Penning trap mass spectrometry at TRIGA-TRAP

The highest precision in the determination of nuclear and atomic masses can be achieved by Penning trap mass spectrometry. The mass value is obtained through a measurement of the cyclotron frequency of the stored charged particle. Two different approaches are used at the Penning trap mass spectrometer TRIGA-TRAP for the mass determination: the destructive Time-Of-Flight Ion Cyclotron Resonance (TOF-ICR) technique and the non-destructive Fourier Transform Ion Cyclotron Resonance (FT-ICR) method. New developments for both techniques are described, which will improve the detection efficiency and the suppression of contaminations in the case of TOF-ICR. The FT-ICR detection systems will allow for the investigation of an incoming ion bunch from a radioactive-beam facility on the one hand, and for the detection of a single singly charged ion in the Penning trap on the other hand.

High-precision masses of neutron-deficient rubidium isotopes using a Penning trap mass spectrometer

The atomic masses of the neutron-deficient radioactive rubidium isotopes $^{74\ensuremath{-}77,79,80,83}\mathrm{Rb}$ have been measured with the Penning trap mass spectrometer ISOLTRAP. Using the time-of-flight cyclotron resonance technique, relative mass uncertainties ranging from $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ to $5.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ were achieved. In all cases, the mass precision was significantly improved as compared with the prior Atomic-Mass Evaluation; no significant deviations from the literature values were observed. The exotic nuclide $^{74}\mathrm{Rb}$, with a half-life of only 65 ms, is the shortest-lived nuclide on which a high-precision mass measurement in a Penning trap has been carried out. The significance of these measurements for a check of the conserved-vector-current hypothesis of the weak interaction and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix is discussed.

Optically detected cyclotron resonance studies of InxGa1−xNyAs1−y∕GaAs quantum wells sandwiched between type-II AlAs∕GaAs superlattices

We report on our results from a systematic study of layered structures containing an InGaNAs∕GaAs single quantum well (SQW) enclosed between staggered type II AlAs∕GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, the predominant ODCR peak is shown to be related to carriers with a two-dimensional character and a cyclotron resonance effective mass of m*≈(0.51–0.56)m0. The responsible carriers are ascribed to electrons on the ellipsoidal equienergy surface at the AlAs X point of the Brillouin zone within the SL, based on results from angular and spectral dependences of the ODCR signal. No ODCR signal related to the InGaNAs SQW was detected, presumably due to low carrier mobility despite the high optical quality. Multiple absorption of photons with energy below the band gap energy of the SL and the GaAs barriers was observed, which bears implication on the efficiency of light-emitting devices based on these structures.

Fundamentals of Molecular Formula Assignment to Ultrahigh Resolution Mass Data of Natural Organic Matter

Ultrahigh-resolution mass spectrometry via the Fourier transform ion cyclotron resonance technique (FT-ICR-MS) allows the identification of thousands of different molecular formulas in natural organic matter and petroleum samples. Molecular formula assignment from mass data is most critical and time-consuming for these samples, and in many cases, several formulas can be determined for the same molecular mass. Therefore, automated procedures are required for an efficient exploitation of the extensive data sets. Here, we revise statements in a recent publication,1 which might result in a misleading impression about our approach of formula assignment in a previous work. We also summarize and categorize existing procedures for formula assignment. In addition, we propose new techniques, which are suitable to be implemented in automated evaluation software. The homologous series approach is extended toward a building block approach that can be applied as a new exclusion criterion for incorrect formula assignments. The examination of stable isotope ratios of individual molecules in natural organic matter can be applied as an additional and intrinsic evaluation for calculated molecular formulas.

Screening and confirmation criteria for hormone residue analysis using liquid chromatography accurate mass time-of-flight, Fourier transform ion cyclotron resonance and orbitrap mass spectrometry techniques

An emerging trend is recognised in hormone and veterinary drug residue analysis from liquid chromatography tandem mass spectrometry (LC/MS/MS) based screening and confirmation towards accurate mass alternatives such as LC coupled with time-of-flight (TOF), Fourier transform ion cyclotron resonance (FTICR) or Fourier transform orbitrap (FT Orbitrap) MS. In this study, mass resolution and accuracy are discussed for LC/MS screening and confirmation of targeted analytes and for the identification of unknowns using the anabolic steroid stanozolol and the designer β-agonist “Clenbuterol-R” as model substances. It is shown theoretically and experimentally that mass accuracy criteria without proper mass resolution criteria yield false compliant (false negative) results, both in MS screening and MS/MS confirmation of stanozolol. On the other hand, previous medium resolution accurate mass TOFMS/MS data of the designer β-agonist were fully confirmed by high resolution FT Orbitrap MSn experiments. A discussion is initiated through a proposal for additional criteria for the use of accurate mass LC/MS technologies, to be implemented in Commission Decision 2002/657/EC.

Thermogenic organic matter dissolved in the abyssal ocean

Formation and decay of thermogenic organic matter are important processes in the geological carbon cycle, but little is known about the fate of combustion-derived and petrogenic compounds in the ocean. We explored the molecular structure of marine dissolved organic matter (DOM) for thermogenic signatures in different water masses of the Southern Ocean. Ultrahigh-resolution mass spectrometry via the Fourier transform-ion cyclotron resonance technique (FT-ICR-MS) revealed the presence of polyaromatic hydrocarbons (PAHs) dissolved in the abyssal ocean. More than 200 different PAHs were discerned, most of them consisting of seven condensed rings with varying numbers of carboxyl, hydroxyl, and aliphatic functional groups. These unambiguously thermogenic compounds were homogenously distributed in the deep sea, but depleted at the sea surface. Based on the structural information alone, petrogenic and pyrogenic compounds cannot be distinguished. Surface depletion of the PAHs and first estimates for their turnover rate (> 1.2 · 10 12 mol C per year) point toward a primarily petrogenic source, possibly deep-sea hydrothermal vents, which is thus far speculative because the fluxes of combustion-derived and petrogenic matter to the ocean are not well constrained. We estimate that > 2.4% of DOM are thermogenic compounds, and their global inventory in the oceans is > 1.4 · 10 15 mol C, significantly impacting global biogeochemical cycles.

Use of electron cyclotron resonance x-ray source for nondestructive testing application

Electron cyclotron resonance (ECR) technique is being used for generating x rays in the low-energy region (<150keV). Recently, the source is used for the calibration of thermoluminescent dosimetry (TLD) badges. In order to qualify the ECR x-ray source for imaging application, the source should give uniform flux over the area under study. Lead collimation arrangement is made to get uniform flux. The flux profile is measured using a teletector at different distance from the port and uniform field region of 10×10cm2 has been marked at 20cm from the x-ray exit port. A digital-to-analog converter (DAC) circuit pack is used for examining the source performance. The required dose for nondestructive testing examination has been estimated using a hospital x-ray machine and it is found to be 0.05mSv. Our source experimental parameters are tuned and the DAC circuit pack was exposed for nearly 7min to get the required dose value. The ECR x-ray source operating parameters are argon pressure: 10−5Torr, microwave power: 350W, and coil current: 0A. The effective energy of the x-ray spectrum is nearly 40keV. The x-ray images obtained from ECR x-ray source and hospital medical radiography machine are compared. It is found that the image obtained from ECR x-ray source is suitable for NDT application.

Formation of mixed Fe-Mo oxo clusters in the gas phase

Reactions of oxygen-containing molybdenum clusters MoxOy (x = 1–3, y = 1–9) with iron carbonyl ions Fe(CO) n + (n = 1–3) were studied by the ion cyclotron resonance technique. The reactions were found to yield mixed Fe-Mo oxo clusters MoxOyFe+ (x = 2, 3; y = 5, 6, 8, 9).