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  • 1. Bernigaud, Virgile
    et al.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Hvelplund, Preben
    Kadhane, Umesh
    Larsen, Mikkel Koefod
    Manil, Bruno
    Nielsen, Steen Bröndsted
    Panja, Subhasis
    Ptasinska, Sylwia
    Rangama, Jimmy
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Streletskii, Alexey V.
    Stöchkel, Kristian
    Worm, Esben S.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Electron capture-induced dissociation of AK dipeptide dications: Influence of ion velocity, crown-ether complexation and collision gas2008In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 276, no 2-3, p. 77-81Article in journal (Refereed)
    Abstract [en]

    The fragmentation of doubly protonated AK dipeptide ions has been investigated after collisional electron transfer. Electron capture leads to three dominant channels, H loss, NH3 loss, and N–Cα bond breakage to give either c+ or z+ fragment ions. The relative importance of these channels has been explored as a function of ion velocity, the degree of complexation with crown ether, and collision gas. Our results indicate that H loss and NH3 loss are competing channels whereas the probability of N–Cα bond breakage is more or less constant.

  • 2.
    Haag, Nicole
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Brøndsted Nielsen, Steen
    Hvelplund, Preben
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Electron capture induced dissociation of doubly protonated pentapeptides: Dependence on molecular structure and charge separation2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 3, p. 035102-Article in journal (Refereed)
    Abstract [en]

    We have studied electron capture induced dissociation of a set of doubly protonated pentapeptides, all composed of one lysine (K) and either four glycine (G) or four alanine (A) residues, as a function of the sequence of these building blocks. Thereby the separation of the two charges, sequestered on the N-terminal amino group and the lysine side chain, is varied. The characteristic cleavage of N–Cα bonds is observed for all peptides over the whole backbone length, with the charge carrying fragments always containing K. The resulting fragmentation patterns are very similar if G is replaced by A. In the case of [XKXXX+2H]2+ (X=A or G), a distinct feature is observed in the distribution of backbone cleavage fragments and the probability for ammonia loss is drastically reduced. This may be due to an isomer with an amide oxygen as protonation site giving rise to the observed increase in breakage at a specific site in the molecule. For the other peptides, a correlation with the distance between amide oxygen and the charge at the lysine side chain has been found. This may be an indication that it is only the contribution from this site to the charge stabilization of the amide π* orbitals which determines relative fragment intensities. For comparison, complexes with two crown ether molecules have been studied as well. The crown ether provides a shielding of the charge and prevents the peptide from folding and internal hydrogen bonding, which leads to a more uniform fragmentation behavior.

  • 3.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 4, p. 044301-Article in journal (Refereed)
    Abstract [en]

    We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H+-, C2H2-, and C2H2+-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion-PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAHq+-molecules are thermodynamically stable for q <= 2 (naphthalene, biphenylene, and anthracene), q <= 3 (pyrene), and q <= 4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H+-emissions from all five PAHs and for C2H2+-emission from naphthalene - the smallest PAH.

  • 4.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kohler, Bern
    Hoffmann, Soren Vronning
    Nielsen, Steen Brondsted
    Synchrotron Radiation Circular Dichroism of Various G-Guadruplex Structures2010In: Biopolymers, ISSN 0006-3525, E-ISSN 1097-0282, Vol. 93, no 5, p. 429-433Article in journal (Refereed)
    Abstract [en]

    Here we report synchrotron radiation circular dichroism spectra of various G-quadruplexes from 179 to 350 nm, and a number of bands in the vacuum ultraviolet (VUV) are reported for the first time. For a tetramolecular parallel structure, the strongest band in the spectrum is a negative band in the VUV at 182 nm; for a bimolecular antiparallel structure with diagonal loops, a new strong positive band is found at 190 nm; for a bimolecular parallel structure with edgewise loops, a strong positive band at 189 nm is observed; and for a self-folded chair-type structure, the strongest band in the spectrum is a positive band at 187 nm. For the tetramolecular parallel structure, the CD signals at all wavelengths are dominated by contributions from quartets of G bases, and the signal strength is approximately proportional to the number of quartets. Our experiments on well-characterized G-quadruplex structures lead us to question past attributions of CD signals to helix handedness and G quartet polarity. Although differences can be observed in the VUV region for the various quadruplex types, there do not appear to be clear-cut spectral features that can be used to identify specific topological features. It is suggested that this is because a dominant positive band in the VUV seen near 190 nm in all quadruplex structures is due to intrastrand guanine guanine base stacking. However, our spectra can serve as reference spectra for the G-quadruplex structures investigated and, not least, to benchmark theoretical calculations and empirical models.

  • 5.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nielsen, Lisbeth M.
    Kohler, Bern
    Hoffman, Soren Vronning
    Nielsen, Steen Brondsted
    Electronic coupling between cytosine bases in DNA single strands and i-motifs revealed from synchrotron radiation circular dichroism experiments2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 14, p. 3426-3430Article in journal (Refereed)
    Abstract [en]

    In this work we have recorded synchrotron radiation circular dichroism (SRCD) spectra from 180 nm to 360 nm of cytosine strands [(dC)(n), n = 1, 2,..., 10] in aqueous solution at different pH values to reveal electronic coupling between bases in different ionisation states. The geometry of the strands is determined by the pH value and the strand length and the local organisation of the cytosines will determine the base-to-base interaction that impacts on the CD signal. At low pH where all bases are protonated, there is no signature of electronic coupling between the bases, and the SRCD spectrum is simply n times that of the n = 1 spectrum. At higher pH where all bases are neutral, the spectra for n > 1 differ from the monomer spectrum, which implies electronic coupling between bases. The correlation between the CD signal and n is linear, and the spatial extent of the excited state wavefunction is therefore over just two stacked bases both in the UV and VUV. At intermediate pH, the low-n spectra are different from the high-n spectra, and a transition is seen to occur at n = 6-8. We ascribe this behavior to the formation of i-motif structures between four (dC)(n) strands for high n.

  • 6.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Adoui, L.
    Mery, A.
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, no 21, p. 213401-Article in journal (Refereed)
    Abstract [en]

    We report the first experimental study of ions interacting with clusters of polycyclic aromatic hydrocarbon (PAH) molecules. Collisions between 11.25 keV He-3(+) or 360 keV Xe-129(20+) and weakly bound clusters of one of the smallest PAH molecules, anthracene, show that C14H10 clusters have much higher tendencies to fragment in ion collisions than other weakly bound clusters. The ionization is dominated by peripheral collisions in which the clusters, very surprisingly, are more strongly heated by Xe20+ collisions than by He+ collisions. The appearance size is k = 15 for [C14H10](k)(2+).

  • 7.
    Holm, Anne Ivalu Sander
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nielsen, Lisbeth Munksgaard
    Hoffmann, Søren Vrønning
    Nielsen, Steen Brøndsted
    Vacuum-ultraviolet circular dichroism spectroscopy of DNA: a valuable tool to elucidate topology and electronic coupling in DNA2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 33, p. 9581-9596Article in journal (Refereed)
    Abstract [en]

    Circular dichroism (CD) is a powerful technique to obtain information on electronic transitions and has been used extensively for studies on DNA. Most experiments are done in the UV region but new information is often revealed from extending the wavelength region down into the vacuum ultraviolet (VUV) region. Such experiments are most easily carried out with synchrotron radiation (SR) light sources that provide large photon fluxes. Here we provide a summary of the SRCD data taken on different DNA strands with emphasis on results from our own laboratory within the last five years.(1-3) Signal intensities in the VUV are often significantly larger than those in the UV, and the electronic coupling between bases may increase with excitation energy. CD spectroscopy is particularly useful for investigating the extent of electronic coupling within a strand, i.e., the degree of delocalisation of the excited-state electronic wavefunction. The spatial extent of the wavefunction may be limited to just one base or it extends over two or more bases in a stack or between bases on different strands.(4,5) The actual character of the electronically excited state is linked to base composition and sequence as well as DNA folding motif (A-, B-, Z-DNA, triplexes, quadruplexes, etc.). The latter depends on experimental conditions such as solution acidity, temperature, ionic strength, and solvent.

  • 8.
    Johansson, Henrik A. B.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Brøndsted Nielsen, S.
    Wyer, J. A.
    Kirketerp, M.-B. S.
    Støchkel, K.
    Hvelplund, P.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Unimolecular dissociation of anthracene and acridine cations: The importance of isomerization barriers for the C2H2 loss and HCN loss channels2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, p. 084304-Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Johansson, Henrik A. B.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Lawicki, A.
    Capron, M.
    Domaracka, A.
    Lattouf, E.
    Maclot, S.
    Maisonny, R.
    Manil, B.
    Chesnel, J.-Y.
    Adoui, L.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 4, p. 043201-Article in journal (Refereed)
    Abstract [en]

    We report on an experimental study of the ionization and fragmentation of clusters of k polycyclic aromatic hydrocarbon (PAH) molecules using anthracene, C14H10, or coronene, C24H12. These PAH clusters are moderately charged and strongly heated in small impact parameter collisions with 22.5-keV He2+ ions, after which they mostly decay in long monomer evaporation sequences with singly charged and comparatively cold monomers as dominating end products. We describe a simple cluster evaporation model and estimate the number of PAH molecules in the clusters that have to be hit by He2+ projectiles for such complete cluster evaporations to occur. Highly charged and initially cold clusters are efficiently formed in collisions with 360-keV Xe20+ ions, leading to cluster Coulomb explosions and several hot charged fragments, which again predominantly yield singly charged, but much hotter, monomer ions than the He2+ collisions. We present a simple formula, based on density-functional-theory calculations, for the ionization energy sequences as functions of coronene cluster size, rationalized in terms of the classic electrostatic expression for the ionization of a charged conducting object. Our analysis indicates that multiple electron removal by highly charged ions from a cluster of PAH molecules rapidly may become more important than single ionization as the cluster size k increases and that this is the main reason for the unexpectedly strong heating in these types of collisions.

  • 10. Lawicki, A.
    et al.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Maclot, S.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Manil, B.
    Adoui, L.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, B. A.
    Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 83, no 2, p. 022704-Article in journal (Refereed)
    Abstract [en]

    The interaction of multiply charged ions (He2+, O3+, and Xe20+) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C24H12) and pyrene (C16H10) is studied for low-velocity collisions (v <= 0.6 a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, n, in the intensity distributions of the CnHx+ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C60 collisions. The latter oscillations are known to be due to dissociation energy differences between even-and odd-n Cn-chain molecules. For PAH molecules, the average numbers of H atoms attached to the CnHx chains are larger for even-n reflecting acetylenic bond systems.

  • 11. Nielsen, Lisbeth Munksgaard
    et al.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Hoffmann, Sören Vronning
    Nielsen, Steen Brondsted
    Effect of introducing thymine spacers into an adenine strand: Electronic decoupling?2011In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 220, no 1, p. 1-3Article in journal (Refereed)
    Abstract [en]

    Electronic coupling between DNA bases governs the deexcitation pathways after light absorption as well as the ability of the DNA strand to conduct charge. UV excitation of single strands of adenine bases involves two adjacent bases while the spatial extent of the excited state wavefunction following VUV excitation is over eight bases. In this work, we have recorded synchrotron radiation circular dichroism spectra for a series of DNA strands on the form A(n)T(m)A(n), n = 1-5 and m = 1-3, in aqueous solution to study the effect of introducing thymine spacers on the electronic coupling between the adenines. We find that a single thymine spacer is enough to eliminate the strong coupling between the adenine bases for all excitation wavelengths between 175 nm and 330 nm.

  • 12. Rousseau, P.
    et al.
    Lawicki, A.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Capron, M.
    Maisonny, R.
    Maclot, S.
    Lattouf, E.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Mery, A.
    Rangama, J.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, S.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Chesnel, J. -Y
    Domaracka, A.
    Manil, B.
    Adoui, L.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, B. A.
    Low energy ions interacting with anthracene molecules and clusters2012In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 279, p. 140-143Article in journal (Refereed)
    Abstract [en]

    The interaction of slow ions (nu similar to 0.4 au.) with a small polycyclic aromatic hydrocarbon, namely anthracene (C14H10), is studied in the gas-phase either with the isolated molecule or with a pure cluster target. We discuss the ionization and fragmentation of the molecule with respect to the projectile charge state, i.e. for singly charged He+ ions and for multiply charged Xe20+. ions. For the isolated C14H10, single or multiple ionization of the molecule occurs under ion impact. The (multi) cation relative yields are compared with those obtained by other ionization methods (electron and fs-laser). The molecular dissociation occurs by loss of hydrogen and small hydrocarbon molecules, leading to the formation of CnHx cations. The interaction of Xe20+ with C14H10 clusters gives surprising results, i.e. the emission of hotter monomer compared to the interaction with He+.

  • 13.
    Seitz, Fabian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Domaracka, A.
    Adoui, L.
    Mery, A.
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Polycyclic aromatic hydrocarbon-isomer fragmentation pathways: Case study for pyrene and fluoranthene molecules and clusters2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, no 6, p. 064302-Article in journal (Refereed)
    Abstract [en]

    We report on measurements of the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) targets in Xe(20+) + C(16)H(10) and Xe(20+) + [C(16)H(10)](k) collisions and compare results for the two C(16)H(10) isomers: pyrene and fluoranthene. For both types of targets, i.e., for single PAH molecules isolated in vacuum or for isomerically pure clusters of one of the molecules, the resulting fragment spectra are surprisingly similar. However, we do observe weak but significant isomer effects. Although these are manifested in very different ways for the monomer and cluster targets, they both have at their roots small differences (<2.5 eV) between the total binding energies of neutral, and singly and multiply charged pyrene and fluoranthene monomers. The results will be discussed in view of the density functional theory calculations of ionization and dissociation energies for fluoranthene and pyrene. A simple classical over-the-barrier model is used to estimate cross sections for single-and multiple-electron transfer between PAHs and ions. Calculated single and multiple ionization energies, and the corresponding model PAH ionization cross sections, are given.

  • 14.
    Thomas, Richard D.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckstrom, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, Department of Physics.
    Das, Susanta
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, H. A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Källersjö, Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Malm, Bo
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Masuda, Masaharu
    Stockholm University, Faculty of Science, Department of Physics.
    Misra, Deepankar
    Stockholm University, Faculty of Science, Department of Physics.
    Orban, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Paál, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, K.
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Weimer, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    The double electrostatic ion ring experiment: A unique cryogenic electrostatic storage ring for merged ion-beams studies2011In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 6, p. 065112-Article in journal (Refereed)
    Abstract [en]

    We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate rings and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.

  • 15.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, Lamri
    Bernigaud, Virgile
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Haag, Nicole
    Stockholm University, Faculty of Science, Department of Physics.
    Holm, Anne I. S.
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Hvelplund, Preben
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics.
    Kadhane, Umesh
    Larsen, Mikkel Kofoed
    Liu, Bo
    Manil, Bruno
    Bröndsted Nielsen, Steen
    Panja, Subhasis
    Rangama, Jimmy
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Stöchkel, Kristian
    Electron-Capture-Induced Dissociation of Microsolvated Di- and > Tripeptide Monocations: Elucidation of Fragmentation Channels from > Measurements of Negative Ions2009In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 10, no 9-10, p. 1619-1623Article in journal (Refereed)
    Abstract [en]

    The branching ratio between ammonia loss and NCα bond cleavage of singly charged microsolvated peptides after electron capture from cesium depends on the solvent molecule attached. Density functional calculations reveal that for [GA+H]+(CE) (G=glycine, A=alanine, CE=crown ether), the singly occupied molecular orbital of the neutral radical is located mainly on the amide group (see picture).

    The results from an experimental study of bare and microsolvated peptide monocations in high-energy collisions with cesium vapor are reported. Neutral radicals form after electron capture from cesium, which decay by H loss, NH3 loss, or NCα bond cleavage into characteristic z. and c fragments. The neutral fragments are converted into negatively charged species in a second collision with cesium and are identified by means of mass spectrometry. For protonated GA (G=glycine, A=alanine), the branching ratio between NH3 loss and NCα bond cleavage is found to strongly depend on the molecule attached (H2O, CH3CN, CH3OH, and 18-crown-6 ether (CE)). Addition of H2O and CH3OH increases this ratio whereas CH3CN and CE decrease it. For protonated AAA ([AAA+H]+), a similar effect is observed with methanol, while the ratio between the z1 and z2 fragment peaks remains unchanged for the bare and microsolvated species. Density functional theory calculations reveal that in the case of [GA+H]+(CE), the singly occupied molecular orbital is located mainly on the amide group in accordance with the experimental results.

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