| 1. |
- Angerer, Tina B., 1987, et al.
(author)
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High energy gas cluster ions for organic and biological analysis by time-of-flight secondary ion mass spectrometry
- 2015
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 377, s. 591-598
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Journal article (peer-reviewed)abstract
- There is considerable excitement surrounding the application of gas cluster ion beams (GCIBs) for SIMS analysis in order to study organic materials and biological samples such as cells and tissues. These ion beams, that often comprise several thousand argon atoms in the primary ion, have been used mainly for the etching of organic materials to remove damage from the surface allowing molecular depth profiling experiments to be performed. The energy of the ion beam is normally 2–20 keV. There have been relatively few studies reported on the use of GCIB as analysis beams, due to difficulties related to fast pulsing and focusing of the beam along with the sometimes low ionisation efficiency. In this study, we report on the use of a new higher energy (40 keV) GCIB operated in a continuous mode. When compared to lower energies depth profiles on thin films of Irganox 1010 show an increase in sputter yield signal while fragmentation, damage accumulation and ionisation efficiency remains unchanged. Experiments on brain tissues show increased signal levels especially for higher mass secondary ions (m/z 500+) in comparison to C60+ at 40 keV and Ar4000+ at 20 keV impact energy. The use of higher energies facilitates better focusing of the primary ion beam as demonstrated here on a human hair sample where we achieve a spatial resolution of
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| 2. |
- Bemis, Kylie A., et al.
(author)
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Statistical detection of differentially abundant ions in mass spectrometry-based imaging experiments with complex designs
- 2019
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In: International Journal of Mass Spectrometry. - : ELSEVIER SCIENCE BV. - 1387-3806 .- 1873-2798. ; 437, s. 49-57
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Journal article (peer-reviewed)abstract
- Mass Spectrometry Imaging (MSI) characterizes changes in chemical composition between regions of biological samples such as tissues. One goal of statistical analysis of MSI experiments is class comparison, i.e. determining analytes that change in abundance between conditions more systematically than as expected by random variation. To reach accurate and reproducible conclusions, statistical analysis must appropriately reflect the initial research question, the design of the MSI experiment, and all the associated sources of variation. This manuscript highlights the importance of following these general statistical principles. Using the example of two case studies with complex experimental designs, and with different strategies of data acquisition, we demonstrate the extent to which choices made at key points of this workflow impact the results, and provide suggestions for appropriate design and analysis of MSI experiments that aim at detecting differentially abundant analytes. (C) 2018 Elsevier B.V. All rights reserved.
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| 3. |
- Delcorte, Arnaud, et al.
(author)
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Re-print of "Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics"
- 2015
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 377:1, s. 580-590
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Journal article (peer-reviewed)abstract
- This article reviews the results of molecular dynamics simulations of cluster sputtering of hydrocarbon polymers obtained in the last few years and expand them with unpublished data of Ar cluster bombardment. The targets are molecular solids of linear hydrocarbons, polyethylene and polystyrene, includingapolyethylene substrate decorated with adsorbed globular macromolecules. The projectiles are (hydro)carbon and Arn clusters, from small tomassive, as well as Bin and Au400 clusters. The study focuses on the dynamics of cratering and sputtering, using a coarse-grained representation of the samples, on the study ofmolecular fragmentation, crosslinking and freeHformation, usingafully atomistic model, and on the conditions of desorption of macromolecules by massive clusters. The results explain the similarities and differences between several cluster types and sizes and, to a large extent, the sputtering yields of Arn clusters and their 'universal' dependence on the scaled cluster energy, as observed in the experiments. They also demonstrate the reduction of sample fragmentation and crosslinking when going to larger clusters and the incidence angle dependence of intact macromolecule emission. Recent experimental validations obtained in our laboratory are also introduced and comparisons with data obtained by other groups are discussed in order to present a more complete picture of the physics of cluster bombardment of organic solids and polymers.
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| 4. |
- Fathi, Pantea, et al.
(author)
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Experimental and theoretical investigations of the ion-neutral reaction of C2H2N+ with C2H6 and implications on chain elongation processes in Titan's atmosphere
- 2016
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 411, s. 1-13
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Journal article (peer-reviewed)abstract
- In this study we report theoretical and experimental evidence for the formation of ionic products by the ion-neutral reaction of C2H2N+ with C2H6. Our investigations consist of laboratory measurements using a guided ion beam mass spectrometer together with complementary ab initio quantum chemical computations, at the MP2/6-311++G(d,p) level of theory, in order to elucidate the energetics and geometries of the intermediates and transition states that are involved in the production of the observed product ions. This study also provides insights on the isomeric nature of the observed product ions, their formation pathways together with collision energy and pressure dependences. The experimental data agrees well with the predictions of the ab initio calculations. Despite data provides evidence for the occurrence of C2H5+ as the most salient product ion, the production of CH3+, C2H3+, C3H5+, C3H7+ and C2H4N+ is also evident. A reaction scheme was proposed to elucidate the mechanisms responsible for the formation of the observed product ions. These processes might be intermediate steps in the generation of long chain carbon and nitrogen-bearing compounds in Titan's ionosphere, the interstellar medium or circumstellar envelopes.
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| 5. |
- Hansen, Klavs, 1958
(author)
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Action spectroscopy of highly excited molecular ions in molecular beams
- 2018
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 430, s. 14-21
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Journal article (peer-reviewed)abstract
- The use of action spectroscopy for quantitative comparisons of different parts of a recorded spectrumrequires that the efficiency of the emission process after photon absorption is quantitatively known. Thequantum yields of measured photo-dissociation processes after photo-absorption are derived here formolecular beams with broad energy distributions. The effect of radiative cooling on the yield is included.The quantum yield for both low energy photons and radiative species shows large variations with photonenergy.
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| 6. |
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| 7. |
- Hansen, Klavs, 1958, et al.
(author)
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Magic numbers and stabilities of heavy water clusters,(D2O)ND+, N = 3 −48
- 2019
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 440, s. 14-19
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Journal article (peer-reviewed)abstract
- The abundance spectrum of deuterated heavy water clusters has been measured, and relative dissociationenergies were extracted from the abundances. The dissociation energies are similar to those of protonatedlight water clusters, except for a slightly reduced excess stability of the N = 21 cluster relative to the N = 22cluster. The difference is interpreted in terms of the special geometry of the N = 21 cluster. The absenceof a similar effect for N = 28/29 suggests that the stability of the N = 28 cluster is not due to a closed shellstructure
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| 8. |
- Hansen, Klavs, 1958
(author)
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The classical capture cross section of an electron and neutral and anionic polarizable molecules with permanent dipole moments
- 2019
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 438, s. 142-147
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Journal article (peer-reviewed)abstract
- tThe energy dependent capture cross sections of electrons and polarizable neutral molecules with perma-nent dipole moments and with and without an additional negative charge are calculated classically. Theresults can be expressed in lengths and energies scaled with parameters that derive from the polarizabil-ity, dipole moment and charge. Cross sections integrated over impact angles are given. The results are ofinterest for both electron attachment and for thermal electron emission. The consequences for thermalelectron emission spectra are discussed quantitatively.
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| 9. |
- Kulyk, Kostiantyn, et al.
(author)
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High-energy collisions of protonated enantiopure amino acids with a chiral target gas
- 2015
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 388, s. 59-64
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Journal article (peer-reviewed)abstract
- We have studied the fragmentation of the singly protonated L- and D-forms of enantiomerically pure phenylalanine (Phe), tryptophan (Trp), and methionine (Met) in high-energy collisions with chiral and achiral gas targets. (S)-(+)-2-butanol, racemic (+/-)-2-butanol, and argon were used as target gases. At center-of-mass frame collision energy of I key, it was found that all of the ions exhibit common fragmentation pathways which are independent of target chirality. For all projectile ions, the elimination of NH3 and H2O + CO were found to be the main reaction channels. The observed fragmentation patterns were dominated by statistically driven processes. The energy deposited into the ions was found to be sufficient to yield multiple fragment ions, which arise from decomposition via various competitive reaction pathways.
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| 10. |
- Marklund, Erik G.
(author)
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Molecular self-occlusion as a means for accelerating collision cross-section calculations
- 2015
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 386, s. 54-55
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Journal article (peer-reviewed)abstract
- A recent article by Béla Paizs in the International Journal of Mass Spectrometry represents an emerging class of “data-oriented†strategies that pre-organise coordinate data to enable faster collision cross-section calculations, the latter being central for the structural interpretation of ion-mobility spectra. The lack of a closed-form expression for the collision cross-section mandates numerical integration, which risks drawing focus from mathematical inspection and thereby precluding the conception of new means to augment the integration. It can be shown from basic geometry and set theory that, within the projection approximation, molecular self-occlusion provides a “theory-oriented†avenue to more efficient collision cross-section calculations, especially when combined with data-oriented acceleration strategies. This approach is particularly suited for the study of macromolecular assemblies and for protein–protein docking, and may further structural biology applications of ion-mobility spectrometry.
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