| 1. |
- Wethekam, S., et al.
(författare)
-
Resonant electron capture by C-60 ions at a metal surface with projected band gap
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:12, s. 121416-
-
Tidskriftsartikel (refereegranskat)abstract
- C-60(+) and C-60(2+) ions are scattered under grazing incidence from an atomically clean and flat Be(0001) surface at kilo-electron-volt energies. Distances for electron transfer are deduced from shifts of angular distributions for incident C-60(+) and C-60(2+) projectiles, which reflect changes in the interaction potentials at the instants of electron transfers. These distances are consistent with classical over-the-barrier model results indicating that the suppression of charge transfer, observed for atomic projectiles in front of metal surfaces with a projected band gap, is absent for fullerenes.
|
|
| 2. |
- Andersson, Ulrika, et al.
(författare)
-
Germline rearrangements in families with strong family history of glioma and malignant melanoma, colon, and breast cancer
- 2014
-
Ingår i: Neuro-Oncology. - : Oxford University Press. - 1522-8517 .- 1523-5866. ; 16:10, s. 1333-1340
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Although familial susceptibility to glioma is known, the genetic basis for this susceptibility remains unidentified in the majority of glioma-specific families. An alternative approach to identifying such genes is to examine cancer pedigrees, which include glioma as one of several cancer phenotypes, to determine whether common chromosomal modifications might account for the familial aggregation of glioma and other cancers. Methods: Germline rearrangements in 146 glioma families (from the Gliogene Consortium; http://www.gliogene.org/) were examined using multiplex ligation-dependent probe amplification. These families all had at least 2 verified glioma cases and a third reported or verified glioma case in the same family or 2 glioma cases in the family with at least one family member affected with melanoma, colon, or breast cancer. The genomic areas covering TP53, CDKN2A, MLH1, and MSH2 were selected because these genes have been previously reported to be associated with cancer pedigrees known to include glioma. Results: We detected a single structural rearrangement, a deletion of exons 1-6 in MSH2, in the proband of one family with 3 cases with glioma and one relative with colon cancer. Conclusions: Large deletions and duplications are rare events in familial glioma cases, even in families with a strong family history of cancers that may be involved in known cancer syndromes.
|
|
| 3. |
- Gatchell, Michael, et al.
(författare)
-
Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions
- 2014
-
Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488:1
-
Konferensbidrag (refereegranskat)abstract
- We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.
|
|
| 4. |
- Gudmundsson, Magnus, et al.
(författare)
-
Angular scattering in fast ion-atom electron transfer collisions : projectile wave diffraction and Thomas mechanisms
- 2010
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:18, s. 185209-
-
Tidskriftsartikel (refereegranskat)abstract
- We report experimental angular differential cross sections for double-electron capture in He2+ + He collisions and single-electron capture in H+ + He collisions for the 1.3-12.5 MeV kinetic energy range. In all cases, the total cross sections are dominated by forward scattering peaks in d sigma/d Omega. The shapes and widths (but not the magnitudes) of these peaks are very similar for all energies and for capture of one or two electrons corresponding also to our measured linear increases in the transverse momentum transfers with increasing projectile velocities. These observations may be ascribed to diffraction limitations which are connected to electron transfer probabilities P(b) which are significant in limited regions of b only. For the H+ + He single-electron capture we observe two additional maxima in the angular differential cross sections. We conclude that while the secondary maxima at similar to 0.5 mrad probably have large contributions from the Thomas proton-electron-nucleus scattering mechanism, the third maxima at similar to 0.75 mrad are most likely mainly due to projectile de Broglie wave diffraction.
|
|
| 5. |
- Chen, Tao, et al.
(författare)
-
Absolute fragmentation cross sections in atom-molecule collisions : Scaling laws for non-statistical fragmentation of polycyclic aromatic hydrocarbon molecules
- 2014
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:22
-
Tidskriftsartikel (refereegranskat)abstract
- We present scaling laws for absolute cross sections for non-statistical fragmentation in collisions between Polycyclic Aromatic Hydrocarbons (PAH/PAH(+)) and hydrogen or helium atoms with kinetic energies ranging from 50 eV to 10 keV. Further, we calculate the total fragmentation cross sections (including statistical fragmentation) for 110 eV PAH/PAH(+) + He collisions, and show that they compare well with experimental results. We demonstrate that non-statistical fragmentation becomes dominant for large PAHs and that it yields highly reactive fragments forming strong covalent bonds with atoms (H and N) and molecules (C6H5). Thus nonstatistical fragmentation may be an effective initial step in the formation of, e. g., Polycyclic Aromatic Nitrogen Heterocycles (PANHs). This relates to recent discussions on the evolution of PAHNs in space and the reactivities of defect graphene structures.
|
|
| 6. |
- da Silva, Humberto, Jr., et al.
(författare)
-
Multiple electron capture, excitation, and fragmentation in C6+-C-60 collisions
- 2014
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 90:3, s. 032701-
-
Tidskriftsartikel (refereegranskat)abstract
- We present experimental and theoretical results on single- and multiple-electron capture, and fragmentation, in C6+ + C-60 collisions at velocities in the v(col) = 0.05 - 0.4 a.u. range. We use time-of-flight mass spectrometry and coincidence detection of charged fragments to separate pure target ionization from processes in which the C-60 target is both ionized and fragmented. The coincidence technique allows us to identify different types of fragmentation processes such as C-60(q+) -> C-58(q+) + C-2 and C-60(q+) -> C-58((q-1)+) + C-2(+). A quasimolecular approach is employed to calculate charge transfer and target excitation cross sections. First-order time-dependent perturbation and statistical methods are used to treat the postcollisional processes: the calculated rate constants for C-2 and C-2(+) emission from the excited and charged fullerene are then used to evaluate the fragmentation dynamics. We show that the target ionization cross section decreases with the induced target charge state and the impact energy. C-2 emission from C-60(q+) is found to dominate when q <= 2 while C-2(+) emission dominates when q >= 5, in agreement with the present and previous experimental results.
|
|
| 7. |
- Fischer, D., et al.
(författare)
-
Importance of Thomas single-electron transfer in fast p-He collisions
- 2010
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:1, s. 12714-
-
Tidskriftsartikel (refereegranskat)abstract
- We report experimental angular differential cross sections for nonradiative single-electron capture in p-He collisions (p + He -> H + He+) with a separate peak at the 0.47 mrad Thomas scattering angle for energies in the 1.3-12.5 MeV range. We find that the intensity of this peak scales with the projectile velocity as v(P)(-11). This constitutes the first experimental test of the prediction from 1927 by L. H. Thomas [Proc. R. Soc. 114, 561 (1927)]. At our highest energy, the peak at the Thomas angle contributes with 13.5% to the total integrated nonradiative single-electron capture cross section.
|
|
| 8. |
- Gatchell, Michael, et al.
(författare)
-
First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE
- 2014
-
Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488
-
Konferensbidrag (refereegranskat)abstract
- We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.
|
|
| 9. |
- Gatchell, Michael, et al.
(författare)
-
Ions colliding with mixed clusters of C-60 and coronene : Fragmentation and bond formation
- 2014
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 90:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied collisions between 22.5 keV He2+ ions and mixed clusters [(C-60)(m)(C24H12)(n)] of m C-60 and n coronene molecules where m and n range up to about ten. Surprisingly, the cluster fragmentation behavior in distant collisions is dramatically different for pure coronene clusters (m = 0) and clusters containing a single C-60 molecule (m = 1). In the latter case, the clusters may be ionized without also being fragmented on the experimental time scale of tens of microseconds. This does not occur for pure coronene clusters, but is a main characteristic of pure fullerene clusters. For ion trajectories penetrating the mixed cluster, we observe covalent bond formations between C-59 or C-58 and C-60, but not between coronene fragments and C-60, or between C-60 fragments and coronene. These results are explained by means of classical molecular dynamics simulations of collisions inside the fragmenting mixed clusters.
|
|
| 10. |
- Gatchell, Michael, et al.
(författare)
-
Ions colliding with polycyclic aromatic hydrocarbon clusters
- 2013
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T156, s. 014062-
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) molecules and their clusters. We find that PAH clusters containing up to roughly 100 individual molecules fragment strongly following collisions with keV ions in low or high charge states (q). For both types of collisions, singly charged PAH molecules are found to be the dominant products but for very different reasons. A high-q ion projectile charge leads to strong multiple ionization of the PAH clusters and subsequent Coulomb explosions. A low-q ion projectile charge often leads to single ionization but stronger internal heating and long evaporation sequences with a singly charged PAH monomer as the end product. We have developed a Monte Carlo method for collision-induced heating of PAH clusters and present an evaporation model where the clusters cool slowly as most of the internal energies are stored in intramolecular vibrations and not in molecule-molecule vibrations.
|
|
