| 1. |
- Gatchell, Michael, et al.
(author)
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Non-statistical fragmentation of PAHs and fullerenes in collisions with atoms
- 2014
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In: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 365, s. 260-265
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Journal article (peer-reviewed)abstract
- Non-statistical fragmentation processes may be important when Polycyclic Aromatic Hydrocarbon molecules (PAHs), fullerenes, or other large complex molecules collide with atoms and atomic ions. For collisions with hydrogen or helium this occurs for center-of-mass energies between a few tens to a few hundreds of electron volts and typically results in losses of single atoms. In such processes one forms much more reactive fragments than in statistical fragmentation, which instead are dominated by losses of C2- or C2H2-molecules (H-atoms) from fullerenes and PAHs, respectively. An enhanced reactivity has recently been demonstrated for van der Waals clusters of C60 molecules where prompt knockouts of single C-atoms from one of the fullerenes yield highly reactive C59+ fragments, which easily form covalent bonds with a C60 molecule inside the clusters
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| 2. |
- Stockett, Mark H., et al.
(author)
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Nonstatistical fragmentation of large molecules
- 2014
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 89:3
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Journal article (peer-reviewed)abstract
- We present experimental evidence for the dominance of prompt single-atom knockout in fragmenting collisions between large polycyclic aromatic hydrocarbon cations and He atoms at center-of-mass energies close to 100 eV. Such nonstatistical processes are shown to give highly reactive fragments. We argue that nonstatistical fragmentation is dominant for any sufficiently large molecular system under similar conditions.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Zettergren, H., et al.
(author)
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Stabilities of multiply charged dimers and clusters of fullerenes
- 2007
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:22, s. 224303-
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Journal article (peer-reviewed)abstract
- The authors find even-odd variations as functions of r (...+[C60]2(r+)([C60C70](r+)) electron-transfer collisions. This even-odd behavior is in sharp contrast to the smooth one for fullerene monomers and may be related to even-odd effects in dimer ionization energies in agreement with results from an electrostatic model. The kinetic energy releases for dimer dissociations [predominantly yielding intact fullerenes [C60]2(r+)-->C60(r1+)+C60(r2+) in the same (r1=r2) or nearby (r1=r2+/-1) charge states] are found to be low in comparison with the corresponding model results indicating that internal excitations of the separating (intact) fullerenes are important. Experimental appearance sizes for the heavier clusters of fullerenes [C60]n(r+) (n>3 and r=2-5) compare well with predictions from a new nearest-neighbor model assuming that r unit charges in [C60]n(r+) are localized to r C60 molecules such that the Coulomb energy of the system is minimized. The system is then taken to be stable if (i) two (singly) charged C60 are not nearest neighbors and (ii) the r C60(+) molecules have binding energies to their neutral nearest neighbors which are larger than the repulsive energies for the (r-1) C60(+)-C60(+) pairs. Essential ingredients in the nearest-neighbor model are cluster geometries and the present results on dimer stabilities.
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| 7. |
- Concina, B., et al.
(author)
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Delayed ionisation of C-76
- 2006
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In: INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. - : Elsevier BV. - 1387-3806. ; 252:2, s. 96-99
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Journal article (peer-reviewed)
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| 8. |
- Fedor, Juray, 1979, et al.
(author)
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Nonthermal power law decay of metal dimer anions
- 2005
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In: Phys. Rev. Lett.. - 0031-9007. ; 94
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Journal article (peer-reviewed)abstract
- The metastable decay of dimer anions of Cu and Ag has been measured in a storage ring. The decay is found to proceed nonexponentially and is well described by a power law with an exponent of -1. This signals the presence of a continuum of decay constants in the ensemble. This quasicontinuum can be provided by the quantum mechanical tunneling decay of high angular momentum states populated in the source. Numerical calculations for dimers of a variety of elements suggest that this decay behavior can be expected for a wide range of species.
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| 9. |
- Hvelplund, P., et al.
(author)
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Stability and Structure of Protonated Clusters of Ammonia and Water, H+(NH3)(m) (H2O)(n)
- 2010
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:27, s. 7301-7310
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Journal article (peer-reviewed)abstract
- Mass spectrometric experiments show that protonated mixed ammonia/water clusters predominant exist in three forms namely H+(NH3)(4)(H2O)(n), H+(NH3)(5)(H2O)(n), and H+(NH3)(6)(H2O)(n) (n = 1-25). For the first two series the collisional activation mass spectra are dominated by loss of water, whereas ions of the latter series preferably lose ammonia. The quantitative characteristics of these observations are reproduced by quantum chemical calculations that also provide insight into the geometrical structures of the clusters. Although the experiments and the calculations agree that clusters with five ammonia are thermodynamically preferred, this does not indicate a rigid tetrahedral structure with one central ammonium covered with an inner solvation shell of four ammonia molecules, with water outside, Instead, water and ammonia have comparable affinities to the binding sites of the first shell, with a preference for ammonia for the first two sites, and water for the last two. The "leftover" ammonia molecules bind equally strong as water molecules to sites in the second shell due to synergistic hydrogen binding. Finally, it is discussed whether the observation of enhanced stability of the H+(NH3)(5)(H2O)(20) in terms of magic numbers and associated geometries may be related to a tetrahedral ammonium core encapsulated in a dodecahedral (H2O)(20) structure, typically found in clathrates.
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| 10. |
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| 11. |
- Johansson, Henrik A. B., et al.
(author)
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Unimolecular dissociation of anthracene and acridine cations : The importance of isomerization barriers for the C2H2 loss and HCN loss channels
- 2011
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 135, s. 084304-
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Journal article (peer-reviewed)abstract
- The loss of C2H2 is a low activation energy dissociation channel for anthracene (C14H10) and acridine (C13H9N) cations. For the latter ion another prominent fragmentation pathway is the loss of HCN. We have studied these two dissociation channels by collision induced dissociation experiments of 50 keV anthracene cations and protonated acridine, both produced by electrospray ionization, in collisions with a neutral xenon target. In addition, we have carried out density functional theory calculations on possible reaction pathways for the loss of C2H2 and HCN. The mass spectra display features of multi-step processes, and for protonated acridine the dominant first step process is the loss of a hydrogen from the N site, which then leads to C2H2/HCN loss from the acridine cation. With our calculations we have identified three pathways for the loss of C2H2 from the anthracene cation, with three different cationic products: 2-ethynylnaphthalene, biphenylene, and acenaphthylene. The third product is the one with the overall lowest dissociation energy barrier. For the acridine cation our calculated pathway for the loss of C2H2 leads to the 3-ethynylquinoline cation, and the loss of HCN leads to the biphenylene cation. Isomerization plays an important role in the formation of the non-ethynyl containing products. All calculated fragmentation pathways should be accessible in the present experiment due to substantial energy deposition in the collisions.
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| 12. |
- Kadhane, U., et al.
(author)
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Near-infrared photoabsorption by C-60 dianions in a storage ring
- 2009
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:1
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Journal article (peer-reviewed)abstract
- We present a detailed study of the electronic structure and the stability of C-60 dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least similar to 1.5 eV. For C-60(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C-60(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C-60 to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11 500 cm(-1) to 13 500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C-60(-) may also be a transition to a cone state.
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| 13. |
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| 14. |
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| 15. |
- Liu, B., et al.
(author)
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Electron capture induced dissociation of nucleotide anions in water nanodroplets
- 2008
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:7, s. 075102-
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Journal article (peer-reviewed)abstract
- We have studied the outcome of collisions between the hydrated nucleotide anion adenosine 5′-monophosphate (AMP) and sodium. Electron capture leads to hydrogen loss as well as water evaporation regardless of the initial number m of water molecules attached to the parent ion (m ⩽ 16). The yield of dianions with microsecond lifetimes increases strongly with m, which is explained from dielectric screening of the two charges by the water nanodroplet. For comparison, collision induced dissociation results in water losses with no or very little damage of the AMP molecule itself.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Sundén, Erika, 1970, et al.
(author)
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Heat capacities of freely evaporating charged water clusters
- 2009
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:22
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Journal article (peer-reviewed)abstract
- We report on evaporation studies on positively charged water clusters (H$^+$(H$_2$O)$_N$) and negatively charged mixed clusters (X$^-$(H$_2$O)$_N$) with a small core ion $X$ ($X$=O$_2$,CO$_3$ or NO$_3$), in the size range $N=5$ to $300$. The clusters were produced by corona discharge in ambient air, accelerated to 50 keV and mass selected by an electromagnet. The loss of monomers during the subsequent 3.4 m free flight was recorded. The average losses are proportional to the clusters' heat capacities and this allowed the determination of size-dependent heat capacities. The values are found to increase almost linearly with clusters size for both species, with a rate of 6-8 $k_B$ per added molecule. For clusters with $N<21$ the heat capacities per molecule are lower but the incremental increase higher. For $N>21$ the values are intermediate between the bulk liquid and the solid water 0 $^o$C values.
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| 20. |
- Sundén, Erika, 1970, et al.
(author)
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Stabilities of protonated water-ammonia clusters
- 2018
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:18
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Journal article (peer-reviewed)abstract
- Branching ratios of water and ammonia evaporation have been measured for spontaneous evaporation from protonated mixed clusters H+(H2On(NH3)(m) in the size range 0 <= n <= 11 and 0 <= m <= 7. Mixed clusters evaporate water except for clusters containing six or more ammonia molecules, indicating the formation of a stable core of one ammonium ion surrounded by four ammonia molecules and a second shell consisting predominantly of water. We relate evaporative branching ratios to free energy differences between the products of competing channels and determine the free energy differences for clusters with up to seven ammonia molecules. Clusters containing up to five ammonia molecules show a very strong scaling of these free energy differences. Published by AIP Publishing.
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| 21. |
- Tomita, S., et al.
(author)
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Dynamic Jahn-Teller effects in isolated C60- studied by near-infrared spectroscopy in a storage ring
- 2005
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In: Phys. Rev. Lett.. - 0031-9007. ; 94
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Journal article (peer-reviewed)abstract
- We have measured the near-infrared absorption spectrum for isolated C ions at room temperature. Two bands, at 9145 cm-1 and 10460 cm-1, have been identified in addition to the main absorption band at 9382 cm-1, seen also at low temperature in a matrix. An interpretation based on the theory of dynamic Jahn-Teller effects is proposed.
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| 22. |
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| 23. |
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| 24. |
- Tomita, S., et al.
(author)
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Lifetimes of C602- and C702- dianions in a storage ring
- 2006
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In: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 124
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Journal article (peer-reviewed)abstract
- C602- and C702- dianions have been produced by electrospray of the monoanions and subsequent electron pickup in a Na vapor cell. The dianions were stored in an electrostatic ring and their decay by electron emission was measured up to 1 s after injection. While C ions are stable on this time scale, except for a small fraction of the ions which have been excited by gas collisions, most of the C ions decay on a millisecond time scale, with a lifetime depending strongly on their internal temperature. The results can be modeled as decay by electron tunneling through a Coulomb barrier, mainly from thermally populated triplet states about 120 meV above a singlet ground state. At times longer than about 100 ms, the absorption of blackbody radiation plays an important role for the decay of initially cold ions. The tunneling rates obtained from the modeling, combined with WKB estimates of the barrier penetration, give a ground-state energy 200±30 meV above the energy of the monoanion plus a free electron and a ground-state lifetime of the order of 20 s.
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| 25. |
- Zettergren, H., et al.
(author)
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Even-odd effects in the ionization cross sections of [C60]2 and [C60C70] dimers
- 2007
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:5, s. 051201-
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Journal article (peer-reviewed)abstract
- We report strong even-odd effects in multiple ionization yields of van der Waals dimers in slowXe30+ + ͓C60͔2͓͑C60C70͔͒ → ̄ + ͓C60͔2r+͓͑C60C70͔r+͒ electron-transfer collisions as functions of r Յ 7. Thisbehavior may be due to even-odd variations in the sequences of dimer ionization energies as calculated with anelectrostatic model including an electrical fullerene-fullerene contact at the 19a0 center-center separation in͓C60͔2+. Prompt dissociations predominantly yield intact fullerenes ͓C60͔2r+ → C60r1+ + C60r2+ in the same͑r1 = r2, even r͒ or nearby ͑r1 = r2 ± 1, odd r Ͼ 1͒ charge states.
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| 26. |
- Zettergren, Henning, et al.
(author)
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Fragmentation and ionization of C70 and C60 by slow ions of intermediate charge
- 2006
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In: European Physical Journal D. - : Springer. - 1434-6060 .- 1434-6079. ; 38:2, s. 299-306
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Journal article (peer-reviewed)abstract
- We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization and fragmentation spectra of C 60 and C70 following collisions with Xe4+ and Kr4+ at v = 0. 06 a.u. Intact positive fullerene ions in charge states up to five (C 5+ 60 and C 5+ 70 ) are produced with both projectiles and for Kr 4++C70 collisions we even observe a small C 6+ 70 peak. The C 3+ 60 /70−2m (m = 1–7) intensity distributions are predominantly associated with the stabilization of three electrons on the projectile ( s = 3) and are significantly different for Xe 4+- and Kr4+ -projectiles. On the other hand, we find remarkable similarities in the C + 3 -C + 11 multi-fragmentation pattern regardless of projectile species (mass) although they are associated with closer encounters in which the projectile is fully neutralized ( s = 4). Simple Monte Carlo calculations of nuclear and electronic loss processes show that both these contributions are very similar in glancing Xe 4++C60 and Kr4++C60 collisions, suggesting that frontal (and more violent) collisions are strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more distant collisions ( s = 3) are projectile mass dependent, while the closer collisions (s = 4) are not. This indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations for slow collisions with singly charged atomic ions rather well) is not valid for a comprehensive description of the energy transfer processes in the present collision systems involving projectiles of higher charge states.
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| 27. |
- Zettergren, Henning, et al.
(author)
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Magic and hot giant fullerenes formed inside ion irradiated weakly bound C-60 clusters
- 2010
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:10, s. 104301-
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Journal article (peer-reviewed)abstract
- We find that the most stable fullerene isomers, C-70-C-94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C-60-molecules. We observe extraordinarily high yields of C-70 and marked preferences for C-78 and C-84. Larger even-size carbon molecules, C-96-C-180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C-70-C-94 mainly are formed by coalescence reactions between small carbon molecules and Coo, while C-n with n >= 96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes.
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| 28. |
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