| 1. |
- Hartman, Henrik, et al.
(författare)
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Negative ion relaxation and reactions in a cryogenic storage ring
- 2020
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Ingår i: Journal of Physics: Conference Series Vol 1412. - : IOP Publishing. - 1742-6588 .- 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- An overview of recent experimental results of studies of negative atomic and molecular ions in the Double ElectroStatic Ion-Ring ExpEriment, DESIREE is given. Metastable level lifetimes in atomic negative ions have been measured by time-dependent laser photodetachment. Rotational relaxation of diatomic anions is studied by near-threshold photodetachment. Spontaneous decays of small metal cluster anions by electron emission and fragmentation is studied with decay-channel specificity. Finally, mutual neutralisation of pairs of negative and positive ions has been investigated with initial and final state selectivity.
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| 2. |
- Najeeb, P. K., et al.
(författare)
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Spontaneous decay of small carbon cluster dianions C-n(2-) (n=7-11)
- 2020
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Ingår i: Journal of Physics, Conference Series, Vol 1412, Article 232014. - : IOP Publishing. - 1742-6588 .- 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- We have studied the stabilities of small carbon dianion clusters, C-n(2-) (n=7-11) in the cryogenic electrostatic ion storage ring, DESIREE. We observe spontaneous electron emission for tens of milliseconds, where dianions containing an even number of carbons decay slower in comparison to their neighbouring cluster sizes. For all the systems considered here, we find that there is a component which is stable at least on the time scales of hundreds of milliseconds.
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| 3. |
- Stockett, M.H., et al.
(författare)
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Spontaneous decay of small copper cluster anions, Cu_N^-, N = 3 - 6
- 2015
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Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; 635
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have measured the spontaneous neutral particle emission from beams of copper cluster anions (Cu_N, N = 3 to 6) stored in an electrostatic storage ring. These experiments have show that multiple structural isomers may be present in the beam.
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| 4. |
- Seitz, Fabian, et al.
(författare)
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Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 139:3
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C-60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C-60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C-60](n)(+) -> C-60(+) + (n - 1)C-60 evaporation model. Excitation energies in the range of only similar to 0.7 eV per C-60 molecule in a [C-60](13)(+) cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2+ and He2+ collisions, we observe very efficient C-119(+) and C-118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C-59(+) or C-58(+) and C-60 during cluster fragmentation. In the Ar2+ case, it is possible to form even smaller C-120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20+ collisions.
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| 5. |
- Wolf, Michael, et al.
(författare)
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PHOTO-STABILITY OF SUPER-HYDROGENATED PAHs DETERMINED BY ACTION SPECTROSCOPY EXPERIMENTS
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 832:1
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the photo-stability of pristine and super-hydrogenated pyrene cations (C16H10+m+, m = 0, 6, or 16) by means of gas-phase action spectroscopy. Optical absorption spectra and photoinduced dissociation mass spectra are presented. By measuring the yield of mass-selected photo-fragment ions as a function of laser pulse intensity, the number of photons (and hence the energy) needed for fragmentation of the carbon backbone was determined. Backbone fragmentation of pristine pyrene ions (C16H10+) requires absorption of three photons of energy just below 3 eV, whereas super-hydrogenated hexahydropyrene (C16H16+) must absorb two such photons and fully hydrogenated hexadecahydropyrene (C16H26+) only a single photon. These results are consistent with previously reported dissociation energies for these ions. Our experiments clearly demonstrate that the increased heat capacity from the additional hydrogen atoms does not compensate for the weakening of the carbon backbone when pyrene is hydrogenated. In photodissociation regions, super-hydrogenated Polycyclic Aromatic Hydrocarbons (PAHs) have been proposed to serve as catalysts for H-2 formation. Our results indicate that carbon backbone fragmentation may be a serious competitor to H-2 formation at least for small hydrogenated PAHs like pyrene.
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| 6. |
- Zettergren, Henning, et al.
(författare)
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Bond formation in C-59(+)-C-60 collisions
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- In this work, we show that keV-ions are able to remove single carbon atoms from individual fullerenes in clusters of C-60 molecules. This very efficiently leads to the formation of exotic q dumbbell molecules through secondary C-59(+) - C-60 collisions within the fragmenting cluster. Such molecular fusion processes are inherently different from those induced by photons where only products with even numbers of carbon atoms are observed. Thus, ion collisions ignite unique and hitherto overlooked secondary reactions in small aggregates of matter. This relates to the question on how complex molecules may form in e.g. space.
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| 7. |
- Ashworth, Eleanor K., et al.
(författare)
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Protomers of the green and cyan fluorescent protein chromophores investigated using action spectroscopy
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 25:30, s. 20405-20413
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Tidskriftsartikel (refereegranskat)abstract
- The photophysics of biochromophore ions often depends on the isomeric or protomeric distribution, yet this distribution, and the individual isomer contributions to an action spectrum, can be difficult to quantify. Here, we use two separate photodissociation action spectroscopy instruments to record electronic spectra for protonated forms of the green (pHBDI(+)) and cyan (Cyan(+)) fluorescent protein chromophores. One instrument allows for cryogenic (T = 40 & PLUSMN; 10 K) cooling of the ions, while the other offers the ability to perform protomer-selective photodissociation spectroscopy. We show that both chromophores are generated as two protomers when using electrospray ionisation, and that the protomers have partially overlapping absorption profiles associated with the S-1 & LARR; S-0 transition. The action spectra for both species span the 340-460 nm range, although the spectral onset for the pHBDI(+) protomer with the proton residing on the carbonyl oxygen is red-shifted by & AP;40 nm relative to the lower-energy imine protomer. Similarly, the imine and carbonyl protomers are the lowest energy forms of Cyan(+), with the main band for the carbonyl protomer red-shifted by & AP;60 nm relative to the lower-energy imine protomer. The present strategy for investigating protomers can be applied to a wide range of other biochromophore ions.
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| 8. |
- Chen, Tao, et al.
(författare)
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Formation of H2 from internally heated polycyclic aromatic hydrocarbons : Excitation energy dependence
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 142:14
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effectiveness of molecular hydrogen (H-2) formation from Polycyclic Aromatic Hydrocarbons (PAHs) which are internally heated by collisions with keV ions. The present and earlier experimental results are analyzed in view of molecular structure calculations and a simple collision model. We estimate that H-2 formation becomes important for internal PAH temperatures exceeding about 2200 K, regardless of the PAH size and the excitation agent. This suggests that keV ions may effectively induce such reactions, while they are unlikely due to, e.g., absorption of single photons with energies below the Lyman limit. The present analysis also suggests that H-2 emission is correlated with multi-fragmentation processes, which means that the [PAH-2H](+) peak intensities in the mass spectra may not be used for estimating H-2-formation rates.
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| 9. |
- Giacomozzi, Linda, et al.
(författare)
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Decay pathways for protonated and deprotonated adenine molecules
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:4
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Tidskriftsartikel (refereegranskat)abstract
- We have measured fragment mass spectra and total destruction cross sections for protonated and deprotonated adenine following collisions with He at center-of-mass energies in the 20-240 eV range. Classical and ab initio molecular dynamics simulations are used to provide detailed information on the fragmentation pathways and suggest a range of alternative routes compared to those reported in earlier studies. These new pathways involve, for instance, losses of HNC molecules from protonated adenine and losses of NH2 or C3H2N2 from deprotonated adenine. The present results may be important to advance the understanding of how biomolecules may be formed and processed in various astrophysical environments.
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| 10. |
- Hartman, Henrik, et al.
(författare)
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First storage of ion beams in the Double Electrostatic Ion-Ring Experiment : DESIREE
- 2013
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 84:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (Cn-, n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2- molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10-14 mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.
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