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The electron-detachment cross section was measured for the molecular negative ions CN- and O-2 incident on N2, in the 0.08-1.2 a.u. velocity region. Our setup uses the gas stripper of a tandem accelerator as a gas chamber. All cross sections present a maximum near 0.4 a.u., a velocity corresponding to the well-known shape-resonance that appears in the electron-N2 collisions. A semiclassical model is employed to analyze the data. The role of this shape resonance is discussed in this article. [ABSTRACT FROM AUTHOR]

We have measured the total electron detachment cross sections of the negative ions C-, CH-, C2-, and C2H- incident on molecular nitrogen in the velocity range 0.22-0.56 a.u. The data were measured with reliable normalization and, particularly in the critical case of the C- projectile, the absence of beam contamination due to long-lived metastable states. Comparison of all measurements of cross sections with experimental data for other projectiles shows a common velocity dependence with a maximum near 0.4 a.u. This behavior suggests a connection between the anion-N2 electron-loss collision dynamics and that of the shape-resonance process dominant in low-velocity electron-N2 total electron scattering. [ABSTRACT FROM AUTHOR]

A recent study of soft x-ray absorption in native and hydrogenated coronene cations, C24H12+m+ m=0-7, led to the conclusion that additional hydrogen atoms protect (interstellar) polycyclic aromatic hydrocarbon (PAH) molecules from fragmentation [Reitsma et ai, Phys. Rev. Lett. 113,053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C16H10+m+, m=0, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules. [ABSTRACT FROM AUTHOR]

We have measured the spontaneous neutral particle emission from copper-cluster anions (Cun-, n = 3-6) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The measured rate of emission from the stored Cu3- ions follows a single power-law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu3 as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu4-, Cu5-, and Cu6- are well described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu6- ions that were excited by 1.13- or 1.45-eV photons after 46 ms of storage. [ABSTRACT FROM AUTHOR]

The intrinsic radiative lifetimes of the 5d106s²S1/2 and 5d96s² ²D3/2 bound excited states in the platinum anion Pt- have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d106s² S1/2 state was measured to be 2.54±0.10s, while only a lifetime in the range of 50-200 ms could be estimated for the 5d96s² D3/2 fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state. [ABSTRACT FROM AUTHOR]

The intrinsic lifetime of the upper level in the bound-bound 3d94s² ²D3/2 → 3d9 4s² ²D5/2 radiative transition in Ni- was measured to be 15.1 ± 0.4s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The storage lifetime of the Ni- ion beam was measured to be close to 5 min at a ring temperature of 13 K. [ABSTRACT FROM AUTHOR]