| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- de Ruette, Nathalie, et al.
(författare)
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DESIREE electrospray ion source test bench and setup for collision induced dissociation experiments
- 2018
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 89:7
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we give a detailed description of an electrospray ion source test bench and a single-pass setup for ion fragmentation studies at the Double ElectroStatic Ion Ring ExpEriment infrastructure at Stockholm University. This arrangement allows for collision-induced dissociation experiments at the center-of-mass energies between 10 eV and 1 keV. Charged fragments are analyzed with respect to their kinetic energies (masses) by means of an electrostatic energy analyzer with a wide angular acceptance and adjustable energy resolution.
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| 3. |
- Feinberg, Alexandra J., et al.
(författare)
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X-ray diffractive imaging of highly ionized helium nanodroplets
- 2022
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Ingår i: Physical Review Research. - 2643-1564. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Finding the lowest energy configuration of N unit charges on a sphere, known as Thomson's problem, is a long-standing query which has only been studied via numerical simulations. We present its physical realization using multiply charged He nanodroplets. The charge positions are determined by x-ray coherent diffractive imaging with Xe as a contrast agent. In neutral droplets, filaments resulting from Xe atoms condensing on quantum vortices are observed. Unique to charged droplets, however, Xe clusters that condense on charges are distributed on the surface in lattice-like structures, introducing He droplets as experimental model systems for the study of Thomson's problem.
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| 4. |
- Gatchell, Michael, et al.
(författare)
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Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation
- 2015
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 92:5
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Tidskriftsartikel (refereegranskat)abstract
- A recent study of soft x-ray absorption in native and hydrogenated coronene cations, C24H12+m + m = 0-7, led to the conclusion that additional hydrogen atoms protect (interstellar) polycyclic aromatic hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C16H10+m +, m = 0, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules.
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| 5. |
- Giacomozzi, Linda, et al.
(författare)
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Knockout driven fragmentation of porphyrins
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19750-19755
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Tidskriftsartikel (refereegranskat)abstract
- We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules.
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| 6. |
- Kulyk, Kostiantyn, et al.
(författare)
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Collision Induced Dissociation of the retinal chromophore Schiff base from sub-eV to keV collision energies
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215.
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Tidskriftsartikel (refereegranskat)abstract
- The gas-phase fragmentation of the protonated n-butylamine Schiff base of all-trans-retinal (NB-RPSB) was measured in low- and high-energy collisional activation modes. The protonated n-butyl β-ionone Schiff base (NB-BISB) peak at m/z = 248, known to be formed as a result of a complex gas-phase rearrangement reaction, has been reported to dominate in mass spectra of NB-RPSB after photo- and collisionally activated fragmentation processes. Earlier reported high-energy collision (50 keV) mass spectra have shown a broad distribution of the fragments with the peak at m/z = 248 present but not dominating. We observed the formation of a peak at m/z = 248 only in collisional activation of NB-RPSB parent ion below a few eV, which shows that the rearrangement process is extremely efficient and happens in a very narrow energy range. On the other hand, our high-energy collision induced dissociation experiments yielded fragmentation patterns, which are fully accounted for simple bond cleavages of the NB-RPSB molecular backbone. We do not observe any peak corresponding to the formation of NB-BISB in the 10 eV – 1 keV collision energy range. This leaves the question open why this fragment reappears in the mass spectra at much higher energies.
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| 7. |
- Stockett, H. Mark, et al.
(författare)
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The threshold displacement energy of buckminsterfullerene and formation of endohedral defect fullerenes
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114.
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the threshold center-of-mass energy for knocking out a single carbon atom from C60 in C60-+He collisions. Combining this experimental result with classical molecular dynamics simulations of such collisions we deduce a semi-empirical value of 24.1±0.5 eV for the C60 → C59+C threshold displacement energy, the minimum energy needed to remove a single carbon atom from the C60 cage. In addition, we oberserve the formation of the endohedral defect fullerene complex He@C59- and its decay product He@C58-.
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| 8. |
- Stockett, Mark H., et al.
(författare)
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The threshold displacement energy of buckminsterfullerene C60 and formation of the endohedral defect fullerene He@C59
- 2018
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 139, s. 906-912
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the threshold center-of-mass kinetic energy for knocking out a single carbon atom from C-60(-) in collisions with He. Combining this experimental result with classical molecular dynamics simulations, we determine a semi-empirical value of 24.1+0.5 eV for the threshold displacement energy, the energy needed to remove a single carbon atom from the C-60 cage. We report the first observation of an endohedral complex with an odd number of carbon atoms, He@C-59(-), and discuss its formation and decay mechanisms.
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| 9. |
- Stockett, Mark H., et al.
(författare)
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Threshold Energies for Single-Carbon Knockout from Polycyclic Aromatic Hydrocarbons
- 2015
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 6:22, s. 4504-4509
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Tidskriftsartikel (refereegranskat)abstract
- We have measured absolute cross sections for ultrafast (femtosecond) single-carbon knockout from polycyclic aromatic hydrocarbon (PAR) cations as functions of He-PAR center-of-mass collision energy in the 10-200 eV range. Classical molecular dynamics (MD) simulations cover this range and extend up to 105 eV. The shapes of the knockout cross sections are well-described by a simple analytical expression yielding experimental and MD threshold energies of E-th(Exp) = 32.5 +/- 0.4 eV and E-th(MD) = 41.0 +/- 0.3 eV, respectively. These are the first measurements of knockout threshold energies for molecules isolated in vacuo. We further deduce semiempirical (SE) and MD displacement energies, i.e., the energy transfers to the PAH molecules at the threshold energies for knockout, of T-disp(SE) = 23.3 +/- 0.3 eV and T-disp(MD) = 27.0 +/- 0.3 eV. The semiempirical results compare favorably with measured displacement energies for graphene (T-disp = 23.6 eV).
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| 10. |
- Wolf, Michael, et al.
(författare)
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Hydrogenated pyrene : Statistical single-carbon loss below the knockout threshold
- 2016
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- An ongoing discussion revolves around the question of what effect hydrogenation has oncarbon backbone fragmentation in polycyclic aromatic hydrocarbons (PAHs). In order to shedmore light on this issue, we have measured absolute single carbon loss cross sections incollisions between native or hydrogenated pyrene cations (C16H+ 10+m , m = 0, 6, 16) and He as functions of center-of-massenergies down to 20 eV. Classical molecular dynamics (MD) simulations give further insightinto energy transfer processes and also yield m-dependent threshold energies for prompt(femtoseconds) carbon knockout. Such fast, non-statistical fragmentation processesdominate CH x -loss for native pyrene (m = 0), while much slowerstatistical fragmentation processes contribute significantly to single-carbon loss for thehydrogenated molecules (m =6 and m =16). The latter is shown by measurements of large CH x -loss crosssections far below the MD knockout thresholds for C16H+ 16 and C16H+ 26.
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