Reflectron Time-of-flight Mass Spectrometer Research Articles

Gas-Phase Preparation of the 14π Hückel Polycyclic Aromatic Anthracene and Phenanthrene Isomers (C14H10) via the Propargyl Addition-BenzAnnulation (PABA) Mechanism.

Polycyclic aromatic hydrocarbons (PAHs) imply the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles, commonly referred to as soot particles in combustion systems and interstellar grains in deep space. Whereas gas phase formation pathways to the simplest PAH - naphthalene (C10H8) - are beginning to emerge, reaction pathways leading to the synthesis of the 14π Hückel aromatic PAHs anthracene and phenanthrene (C14H10) are still incomplete. Here, by utilizing a chemical microreactor in conjunction with vacuum ultraviolet (VUV) photoionization (PI) of the products followed by detection of the ions in a reflectron time-of-flight mass spectrometer (ReTOF-MS), the reaction between the 1'- and 2'-methylnaphthyl radicals (C11H9⋅) with the propargyl radical (C3H3⋅) accesses anthracene (C14H10) and phenanthrene (C14H10) via the Propargyl Addition-BenzAnnulation (PABA) mechanism in conjunction with a hydrogen assisted isomerization. The preferential formation of the thermodynamically less stable anthracene isomer compared to phenanthrene suggests a kinetic, rather than a thermodynamics control of the reaction.

Dissociative photoionization ofm-xylene

The photoionization and dissociative photoionization of m-xylene (C8H10) were researched by using synchrotron radiation vacuum ultraviolet (SR-VUV) and supersonic expanding molecular beam reflectron time-of-flight mass spectrometer (RFTOF-MS) system. The photoionization efficiency spectra (PIEs) of parent ion C8H10+ and main fragment ions C8H9+ and C7H7+ were observed, and the ionization energy (IE) of m-xylene and appearance energies (AEs) of main fragment ions C8H9+ and C7H7+ were determined to be 8.60±0.03 eV, 11.76±0.04 eV and 11.85±0.05 eV, respectively. Structures of reactant, transition states (TSs), intermediates (INTs), and products involved in two dominant dissociation channels were optimized at the B3LYP/6-311++G(d,p) level, and the relative energies were calculated at the G3 level. Based on the results, two major dissociative photoionization channels, C7H7++CH3 and C8H9++H were calculated at the B3LYP/6-311++G(d,p) level. On the basis of theoretical and experimental results, the dissociative photoionization mechanisms of m-xylene were proposed. The C–H or C–C bond dissociation and hydrogen migration are the main processes in the dissociation channels of m-xylene cation.

Investigation of vacuum ultraviolet photoionization of methylcyclohexane in energy region of 9−15.5 eV

Vacuum ultraviolet (VUV) photoionization and photodissociation of methylcyclohexane have been studied utilizing a reflectron time-of-flight mass spectrometer (RTOF-MS) with synchrotron radiation source. Photoionization efficiency curves (PIEs) of molecule ion C7H14+ and fragment ions C7H13+, C6H11+, C6H10+, C5H10+, C5H9+, C4H8+, C4H7+, and C3H5+ were observed. The ionization energy of methylcyclohexane was measured to be (9.80±0.03) eV, and appearance energies of fragment ions were determined from the PIEs. Optimized structures of transitional states, intermediates and product ions were characterized at the B3LYP/6-31G(d) level and the energies were calculated using G3B3 method. Formation channels of dominating fragment ions were proposed. Intramolecular hydrogen migrations and carbon ring-opening were the foremost processes in fragmentation pathways of methylcyclohexane.

Improvement of reflectron time-of-flight mass spectrometer for better convergence of ion beam

Reflectron time-of-flight mass spectrometer (RTOF-MS) is a powerful tool to achieve high resolution in mass analysis of various ions. As it is often supposed that analyte ions are generated in a small volume in the ion-extraction region, its performance is not optimized for ions spread over a large volume. Not only the mass resolution is degraded due to incomplete space and energy focusing, but also the ion beam is subject to significant divergence of ion trajectories after it is reflected from an ion reflector. Here we present a novel design of RTOF-MS equipped with an additional electrostatic lens in front of a conventional grid-less ion reflector for improving convergence of an ion beam. The performance is examined by mass analysis of Ag3+ ions extracted from a volume of 6.3 cm3, i.e., a cylinder with 20-mm length and 20-mm diameter. The improved convergence of an ion beam is demonstrated by a two-dimensional image of ions on the ion detector. Mass resolution is evaluated as well.

Experimental and theoretical study on dissociative photoionization of cyclopentanone

The dissociative photoionization of cyclopentanone was investigated by means of a reflectron time-of-flight mass spectrometer (RTOF-MS) with tunable vacuum ultraviolet synchrotron radiation in the photon energy range of 9.0—15.5 eV. The photoionization efficiency (PIE) curves for molecular ion and fragment ions were measured. The ionization energy of cyclopentanone was determined to be 9.23±0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C5H7O+, C4H5O+, C4H8+/C3H4O+, C3H3O+, C4H6+, C2H4O+, C3H6+, C3H5+, C3H4+, C3H3+, C2H5+ and C2H4+. With the aid of the ab initio calculations at the ωB97X-D/6-31+G(d,p) level of theory, the dissociative mechanisms of C5H8O+ are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.

Photoelectron Spectroscopic and Theoretical Study of Aromatic–Bim Anionic Complexes (Aromatic = C6H5, C5H4N, C4H3O, and C4H4N; m = 1–3): A Comparative Study

The reactions between Bi clusters generated by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The photoelectron (PE) spectra of the dominant anionic products Bi(m)C6H5(-), Bi(m)C5H4N(-) (m = 1-4) and Bi(m)C4H3O(-), Bi(m)C4H4N(-) (m = 1-3) dehydrogenated complexes were obtained by 308 and 193 nm laser, respectively. It was found that the adiabatic electron affinities (EAs) of Bi(m)C4H4N are higher than those of Bi(m)C6H5, Bi(m)C5H4N, and Bi(m)C4H3O with the same metal number m. Theoretical calculations with density functional theory (DFT) were carried out to elucidate the possible structures for Bi(m)C4H4N(-) and Bi(m)C4H4N complexes. By comparison of the theoretical and experimental EAs, the most possible structures were the isomers in which the C4H4N group binds to metal clusters with the N-Bi bond, and their simulated spectra based on Koopmans' theorem were in correct agreement with the PES results. Furthermore, the analysis of the molecular orbital composition provided evidence that the C4H4N group contributes a single electron to bind to Bi(m) clusters with the Bi-N σ bond.

Optimization of mass spectrometers using the adaptive particle swarm algorithm

Optimization of mass spectrometers using the adaptive particle swarm algorithm (APSA) is described along with implementations for ion optical simulations and various time-of-flight (TOF) instruments. The need for in situ self optimization is addressed through discussion of the reflectron TOF mass spectrometer (RTOF) on the European Space Agency mission Rosetta. In addition, a tool for optimization of laboratory mass spectrometers is presented and tested on two different instruments. After the application of APSA optimization, a substantial increase in performance for mass spectrometers that have manually been tuned for several weeks or months is demonstrated.

The coupling of a reflectron time-of-flight mass spectrometer with a cosmic simulation chamber: A powerful new tool for laboratory astrophysics

The addition of an orthogonal reflectron time-of-flight mass spectrometer (ReTOF-MS) to the NASA Ames cosmic simulation chamber (CSC) experiment is described. The simulation chamber contains the elements that produce the molecular species under astrophysically relevant conditions. A pulsed discharge nozzle (PDN) produces ions, neutrals and radicals in a plasma discharge, which are then expanded and supersonically cooled into the chamber. The coupling of the ReTOF-MS to the CSC provides real-time identification of the species, including cations and neutrals, formed in the plasma, an insight into the chemical pathways of the species reacting in the plasma, and an efficient method for the quick determination of the species present in the plasma, which can then be probed spectroscopically with the cavity ring-down spectrometer (CRDS). The combination of the ReTOF-MS, CRDS and PDN components into a single instrument offers a powerful tool, which can be used to probe a variety of different astrophysical environments such as interstellar clouds and planetary atmospheres. The experimental details and representative mass spectra are presented for plasmas generated in combinations of argon and methane samples. These mass spectra show the unambiguous detection of externally generated ions from the plasma in the simulation chamber. In addition, the various spectra show evidence of fragmentation and bond forming reactivity, illustrating the impact of the composition of the plasma.

Photoelectron Spectroscopic and Theoretical Study of Aromatics−Pbm Anionic Complexes (Aromatics = C6H5, C5H4N, C4H3O, and C4H4N; m = 1−4): A Comparative Study

The reactions between lead vapored by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The adiabatic electron affinities (EAs) of the dominant anionic products PbmC6H5(-), Pb(m)C5H4N(-) (m = 1-4) and Pb(m)C4H3 (-), Pb(m)C4H4N(-) (m = 1-3) dehydrogenated complexes are obtained from the photoelectron spectra with 308 and 193 nm photon, respectively. It is found that the EAs of Pb(m)C4H4N are higher than those of Pb(m)C6H5, Pb(m)C5H4N, and Pb(m)C4H3O with the same metal number m. The possible structures for Pb(m)C4H4N(-) complexes were calculated with density functional theory (DFT) and the most stable structure was confirmed. The adiabatic detachment energies for the most stable structure were in agreement with the experimental PES results. The calculated density of state (DOS) agrees with the experimental PES spectrum well. It was confirmed by the theoretical calculations that the C4H4N group bonds on lead clusters through the Pb-N sigma bond.

Development of a reflectron time-of-flight mass spectrometer for non-destructive analysis of isotope ratios in irradiated B 4C pellets—Test measurements on an unirradiated control rod pellet

A laser mass spectrometric facility is developed using a home-built reflectron time-of-flight mass spectrometer (RTOFMS) to analyze the boron isotopic ratio 10B/ 11B in the irradiated B 4C pellets of the FBTR control rod. Compared to other mass spectrometry-based methods, the present method is practically non-destructive and makes it relatively easier to handle irradiated (radioactive) B 4C pellets through remote operation. The results with inactive samples indicate that the method yields 10B percentage values, accurate to within ±1%.

Reactions of platinum cluster ions with benzene

In this work, the cation and anion products of the reactions between platinum clusters produced by laser ablation and the benzene molecules seeded in argon have been studied using a high-resolution reflectron time-of-flight mass spectrometer (RTOFMS). The dominant cation products are [C(6n)H(6n - k)](+) and [Pt(m)(C(6)H(6))(n)](+) complexes, while the dominant anion products are dehydrogenated species, [C(6)H(5)PtH](-), [PtC(12)H(k)](-) and [Pt(m)C(6)H(4) . . . (C(6)H(6))(n)](-), etc. Some important intermediate structures ([PtC(6)H(6)](+), [Pt(C(6)H(6))(2)](+), [Pt(2)(C(6)H(6))(3)](+), [C(6)H(5)PtH](-), [Pt(2)C(6)H(4)](-), [Pt(3)C(6)H(4)](-) and [Pt(4)C(6)H(4)](-)) have been analyzed using density functional theory (DFT) calculations. Different reaction mechanisms are proposed for platinum cluster cations and anions with benzene, respectively.

Dissociation of biomolecules using a ultraviolet matrix‐assisted laser desorption/ionisation time‐of‐flight/curved field reflectron tandem mass spectrometer equipped with a differential‐pumped collision cell

A commercial matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) instrument equipped with a curved field reflectron (CFR) was modified in order to perform collision-induced dissociation (CID) on a variety of biomolecules. The incorporation of a high-resolution ion gate together with a collision cell within the field-free region allowed tandem mass analysis (MS/MS), without the necessity to decelerate the precursor ions prior to activation. The simultaneous detection of all product ions remained possible by using the CFR. To test the MS/MS performances, ACTH (fragment 1-17), a complex high mannose carbohydrate (Man)(8)(GlcNac)(2) and a lysophosphatidylcholine lipid (18:1) were analysed on the modified instrument. Direct comparison with the low-energy product ion spectra, acquired on a MALDI quadrupole ion trap (QIT) two-stage reflectron time-of flight (ReToF) mass spectrometer, showed significant differences in the types of product ions observed. The additional ions detected were a clear indication of the high-energy fragmentation processes occurring in the collision cell.

Experimental and Theoretical Investigation on Binary Semiconductor Clusters of Bi/Si, Bi/Ge, and Bi/Sn

Bi(m)M(n)- (M = Si, Ge, Sn) binary cluster anions are generated by using laser ablation on mixtures of Bi and M (M = Si, Ge, Sn) samples and studied by reflectron time-of-flight mass spectrometer (RTOF-MS) in the gas phase. Some magic number clusters are present in the mass spectra which indicate that they are in stable structures. For small anions (m + n < or = 6), their structures are investigated with the DFT method and the energetically lowest lying structures are obtained. For the binary anionic clusters with the same composition containing Si, Ge, and Sn, they share similar geometric and electronic structure in the small size except that BiSi3-, BiSi5-, Bi2Si2-, Bi2Si3-, and Bi4Sn2- are different for the lowest energetic structures, and the ground states for all the anions are in their lowest spin states. The calculated VDE (vertical detachment energy) and binding energy confirm the obviously magic number cluster of BiM4- (M = Si, Ge, Sn), which agrees with the experimental results.

Determination of Isotopic Ratio of Boron in Boric Acid Using Laser Mass Spectrometry

A reflectron time-of-flight mass spectrometer (RTOFMS) with a laser ablation ion source was used to determine the isotopic ratio of 10B/11B present in boric acid solutions, using graphite as the matrix. The atom % 10B values obtained were within +/-1% of the actual ones. The determination of the boron isotopic ratio using this method is, in comparison to other methods, faster, less expensive and easier to perform. The results are compared with the values determined using thermal ionization mass spectrometry.

Intracluster ion–molecule reactions of Ti + with ether clusters

The intracluster ion–molecule reactions of Ti +(CH 3OR) n (R = CH 3, n-C 3H 7, n-C 4H 9, t-C 4H 9) complexes produced by the mixing of laser-vaporized plasmas and pulsed supersonic beams were investigated using a reflectron time-of-flight mass spectrometer (RTOFMS). The reactions of Ti + with dimethyl ether clusters were found to be dominated by the CH 3 elimination reaction, which produces Ti +(OCH 3) m (CH 3OCH 3) n clusters ( m = 1–3). The mass spectra resulting from the reactions of Ti + with the other ether clusters indicate the formation of major sequences of heterocluster ions with the formula Ti +(OCH 3) x (OR) y (CH 3OR) n , where x = 1–3 and y = 0–2. These sequences are attributed to the insertion of Ti + ions into the C O bonds of the ether molecules within the heteroclusters, followed by alkyl radical elimination. The prevalence of radical elimination of longer alkyl groups rather than of CH 3 radicals suggests that R elimination from the [CH 3O Ti + R] intermediate is the preferred decomposition pathway after the selective insertion of a Ti + ion into the C O bond of an OR group. Our results also indicate that consecutive insertions of a Ti + ion can occur for up to three precursor molecules. The experiments also show that the molecular eliminations of H 2 and alkanes, resulting from C H and C C bond insertion, respectively, play an increasingly important role as the size of the alkyl group (R) in the ether molecule increases. The reaction energetics and the formation mechanisms of the observed heterocluster ions are also discussed.

A Comparative Study of Cation and Anion Cluster Reaction Products: The Reaction Mechanisms of Lead Clusters with Benzene in Gas Phase

The cation and anion products of the reactions between lead clusters produced in the laser ablation and the benzene molecules seeded in argon were studied by high-resolution reflectron time-of-flight mass spectrometer (RTOFMS). The dominant cation products were Pb/benzene association complexes, while the dominant anion products were dehydrogenated species, [PbmCn]-, [PbmCnHk]-, etc. One important intermediate distinguished in the anion reactions was [Pbm(C6H5)]- product. Two conspicuously different and independent reaction mechanisms were proposed for lead cluster cations and anions, respectively.

Gas-phase activation of silane, disilane and germane by actinide ions; and collision induced dissociation of metal oxide ions in TOF-MS

Gas-phase reactions of selected actinide metal ions, An +, with silane, disilane and germane under minimally hyperthermal conditions were studied using a reflectron time-of-flight mass spectrometer (RTOF-MS). Both U + and Np + reacted with silane while Pu + was comparatively inert. The primary reactions with silane yielded the silylenes, AnSiH 2 +; secondary reactions gave AnSi 2H 4 + and AnSi 2H 2 + (An=U, Np). With disilane, single- and double-dehydrogenation by An + produced AnSi 2H 4 + and AnSi 2H 2 + for An=U and Np, while Pu + and Am + were inert. Oxo-ligation rendered plutonium reactive towards silane: UO +, NpO + and PuO + each dehydrogenated disilane to give AnOSi 2H 4 +. With germane, selected lanthanide ions, M +Ln +, were studied along with M +An +. Germylenes, MGeH 2 +, were formed for M=Th, U, Np, Pu, Ce and Tb, while Am + and Tm + were inert. Secondary products were MGe 2 + (M=Th, U, Np, Ce and Tb), ThGe 3 + and ThGe 4 +. The results are assessed in the context of the electronic structures and energetics of the actinide (and lanthanide) ions. For comparison and to confirm consistency with previous studies, a few reactions of CH 4 and C 2H 6 with actinide ions were examined. The nature of anomalous peaks at ion flight times corresponding to “tetrahydride” ions, “AnH 4,” upon introduction of both reactive and inert gases into the reaction region was examined in detail. It was concluded that these aberrant peaks were due to high-energy collision induced dissociation of actinide oxide ions, AnO +, in the first field-free region of the RTOF-MS. The identification of this dissociation phenomenon nullifies a previous report of actinide hydride ions produced by reactions of An + with ethylene oxide.

Ultrafast laser analysis of nitro-PAHs using laser desorption/femtosecond ionization mass spectrometry

Analytical interest in nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) is related to their high mutagenicity and potential presence in a variety of environmental media such as diesel exhaust and urban air particulate matter. Furthermore, fundamental interest in these molecular systems stems from the photophysics of the labile NO2 functional group, which has been investigated using mass spectrometry. The nitro-PAHs, 1-nitronaphthalene, 9-nitroanthracene, and 1-nitropyrene, have been studied using both femtosecond (λ = 395 and 790 nm) and nanosecond (λ = 266 nm) lasers coupled to a reflectron time of flight mass spectrometer. Analysis of mass spectra taken over a range of intensities (1014–1015 W/cm2) has demonstrated that structurally specific ions can be observed for each molecule, with little or no fragmentation at lower intensities. It has also been found that an intact parent ion can be detected using femtosecond ionization at 395 nm in each case. This work demonstrates the potential use of laser desorption/femtosecond laser mass spectrometry (LD/FLMS) as an analytical technique for the detection of nitro-PAHs and other environmental pollutants and as a means of studying the photodynamics of labile molecular systems.

Formation and dissociation of protonated pyridine–methanol cluster ions at 355 and 266 nm

The multi-photon ionization process of the hydrogen-bond cluster of pyridine–methanol has been investigated using a conventional and reflectron time-of-flight mass spectrometer (RTOF-MS) at 355 and 266 nm laser wavelengths, respectively. The sequences of the protonated cluster ions (CH 3OH) n H + and (C 5H 5N n )(CH 3OH) m H + ( n=1,2) were observed at both laser wavelengths, while the sequence of the cluster ions (CH 3)OH n (H 2O)H + was observed only at 355 nm laser wavelength. The difference between the relative signal intensities of the protonated methanol cluster ions at different laser wavelengths is attributed to different photoionization mechanisms. Some nascent cluster ions in metastable states dissociated during free flight to the detector. The dissociation kinetics is also discussed.

Ideal velocity focusing in a reflectron time-of-flight mass spectrometer

A single-stage ion mirror in a time-of-flight (TOF) mass spectrometer (MS) can perform first order velocity focusing of ions initially located at a start focal plane while second order velocity focusing can be achieved using a double-stage reflectron. The situation is quite different when an ion source extraction field is taken into account. In this case which is common in any practical matrix-assisted laser desorption/ionization (MALDI) TOF-MS a single-stage reflectron, for example, cannot perform velocity focusing at all. In this paper an exact, analytic solution for an electric field inside a one-dimensional reflectron has been found to achieve universal temporal focusing of ions having an initial velocity distribution. The general solution is valid for arbitrary electric field distributions in the upstream (from the ion source to the reflectron) and downstream (from the reflectron to an ion detector) regions and in a decelerating part of the reflectron of a reflectron TOF mass spectrometer. The results obtained are especially useful for designing MALDI reflectron TOF mass spectrometers in which the initial velocity distribution of MALDI ions is the major limiting factor for achieving high mass resolution. Using analytical expressions obtained for an arbitrary case, convenient working formulas are derived for the case of a reflectron TOF-MS with a dual-stage extraction ion source. The special case of a MALDI reflectron TOF-MS with an ion source having a low acceleration voltage (or large extraction region) is considered. The formulas derived correct the effect of the acceleration regions in a MALDI ion source and after the reflectron before detecting ions.