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We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p5 2P°1/2 → 3p5 2P°3/2 spontaneous radiative decay in 32S- to be 503 ± 54 sec. This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10-14 mbarat 13 Kand storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 13δ from the only available theoretical prediction [P. Andersson et al., Phys. Rev. A 73, 032705 (2006)]. [ABSTRACT FROM AUTHOR]

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C60 fullerenes. Surprisingly, C+119and C+118are the dominant molecular fusion products. We use molecular dynamics simulations to show that C+59 and C+58ions-effectively produced in prompt knockout processes with He2+-react rapidly with C60 to form dumbbell C+119 and C+118. Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons. [ABSTRACT FROM AUTHOR]

We have measured total absolute cross sections for the mutual neutralization (MN) of O- with O+ and N+. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems, with a multichannel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N++O- collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements. [ABSTRACT FROM AUTHOR]

We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p^{5} ^{2}P_{1/2}^{o}→3p^{5} ^{2}P_{3/2}^{o} spontaneous radiative decay in ^{32}S^{-} to be 503±54  sec. This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10^{-14} mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ from the only available theoretical prediction [P. Andersson et al., Phys. Rev. A 73, 032705 (2006)].

We report experimental total, absolute, fragmentation cross sections for anthracene C14H10, acridine C13H9N, and phenazine C12H8N2 ions colliding with He at center-of-mass energies close to 100 eV. In addition, we report results for the same ions colliding with Ne, Ar, and Xe at higher energies. The total fragmentation cross sections for these three ions are the same within error bars for a given target. The measured fragment mass distributions reveal significant contributions from both delayed (≫10(-12) s) statistical fragmentation processes as well as non-statistical, prompt (∼10(-15) s), single atom knockout processes. The latter dominate and are often followed by secondary statistical fragmentation. Classical Molecular Dynamics (MD) simulations yield separate cross sections for prompt and delayed fragmentation which are consistent with the experimental results. The intensity of the single C/N-loss peak, the signature of non-statistical fragmentation, decreases with the number of N atoms in the parent ion. The fragment intensity distributions for losses of more than one C or N atom are rather similar for C14H10 and C13H9N but differ strongly for C12H8N2 where weak C-N bonds often remain in the fragments after the first fragmentation step. This greatly increases their probability to fragment further. Distributions of internal energy remaining in the fragments after knockout are obtained from the MD simulations.

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C(60) fullerenes. Surprisingly, C(119)(+) and C(118)(+) are the dominant molecular fusion products. We use molecular dynamics simulations to show that C(59)(+) and C(58)(+) ions--effectively produced in prompt knockout processes with He(2+)--react rapidly with C(60) to form dumbbell C(119)(+) and C(118)(+). Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

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 (C(n)(-), 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.

The loss of C(2)H(2) is a low activation energy dissociation channel for anthracene (C(14)H(10)) and acridine (C(13)H(9)N) 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 C(2)H(2) 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 C(2)H(2)/HCN loss from the acridine cation. With our calculations we have identified three pathways for the loss of C(2)H(2) 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 C(2)H(2) 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., (© 2011 American Institute of Physics)

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.

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-C(α) 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.

We have developed a small purely electrostatic ion-beam trap which may be operated in thermal equilibrium at precisely controlled temperatures down to 10 K. Thus, we avoid magnetic field induced mixing of quantum states and may effectively eliminate any influence from absorption of photons from blackbody radiation. We report the first correction-free measurement of the lifetime of the 1s2s2p {4}P{5/2}{0} level of 4He(-) yielding the high-precision result 359.0 +/- 0.7 micros. This result is an essential proof-of-principle for cryogenic electrostatic storage rings and traps for atomic and molecular physics.

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< or =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.

We have used the ion storage ring CRYRING and its internal gas-jet target and recoil-ion-momentum spectrometer to measure absolute cross sections for transfer ionization (TI: p+He-->H0+He2++e(-)) in 2.5-4.5 MeV p-He collisions with separate Thomas (TTI) and kinematic (KTI) TI contributions. The probability for electron emission in kinematical capture decreases with increasing velocity and appears to approach the photoionization shakeoff value (1.63%) [T. Aberg, Phys. Rev. A 2, 1726 (1970)]]. The velocity dependence of the TTI cross section is consistent with the theoretically predicted v(-11) scaling [J. S. Briggs and K. Taulbjerg, J. Phys. B 12, 2565 (1979)]].