A detailed knowledge of the carbon chain’s spectroscopy is of considerable importance in astrophysics. More than two decades ago, Douglas1 put forward the suggestion that the unknown absorbing species responsible for over 150 diffuse interstellar bands, might be long carbon chain molecules, Cn. More recently, Tulej et al.2 measured the gas phase electronic spectrum of the C 7 − chain and found that the 5 narrow absorption bands in the lowest energy transition correlate quite well with the observed wavelengths of narrow diffuse interstellar bands. CRYRING was used to study collision processes between an electron and a negative ion cluster C 4 − . We made use of a grid to separate four neutral channels over the five that contribute to the total neutral 4C production. Only the detachment cross sections, leading to the production of C4, are presented here. Although the doubly charged negative ion C 4 −2 has received little previous attention, a resonance observed in the present work in the threshold region of the detachment cross section is associated with a short lived C 4 −2 state.

In this paper we present the results from two electron scattering experiments performed at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm. First we have studied the cross sections for single, double and triple detachment of Cl-, in the energy range 0 eV to 100eV. Second we have studied electron scattering on C-4(-) ions in the energy range 0 eV to 30eV. The neutral particles from the detachment process was detected, and the different branching ratios were investigated. In particular, we searched for a resonance in the cross section due to the formation of a doubly charged C-4(2-) ions.

CRYRING was used to study collision processes between an electron and a negative ion cluster C-4(-). The total detachment cross sections for the production of the neutral 4C, 3C, 2C, and C fragments were measured. The cross sections for pure detachment, and for detachment plus dissociation leading to the production of C-3+C, 2C(2), and C-2+2C were extracted using a grid. It was found that the pure detachment process overwhelmingly dominates all other fragmentation processes. The threshold location for the detachment channel is found to be around 6.0 eV. Although the doubly charged negative ion C-4(2-) has received little previous attention, a defined near-threshold resonance observed in the detachment cross section curve, has been associated with the short-lived state C-4(2-) (0.7 fs lifetime). (C) 2001 American Institute of Physics.

The radiative lifetimes of the metastable a 9DJ (J = 2–5) levels in Eu II have been measured by laser probing of a stored ion beam. The lifetimes of all four J levels are slightly above 1 s. A deviation from the expected energy dependence of the decay rates for electric quadrupole transitions is observed and discussed.

Electron Impact Single Detachment (EISD) of F- has been studied using the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm, Sweden. F- ions stored in the ring were merged with an electron beam in one of the ring sections. Neutral F atoms produced in the EISD process were detected in the zero-degree direction using a surface barrier detector. The threshold for the detachment process was found to be around 7.6 eV, thus more than twice the binding energy of F-. The cross-sections increased smoothly up to 55 eV where it reached a maximum of 1.9×10 -16 cm 2 . At higher energies a slow decrease of the cross-section was observed, which follows the energy dependence predicted by the Bethe-Born approximation. The experiment showed that CRYRING can be used favourably for studies of anions, and several experiments are forthcoming.

We present the results of an experiment in which electrons have been scattered on CN- ions, over a collision energy range 0–60 eV. The experiment was performed at the heavy ion storage ring CRYRING. The CN- ions were stored in the ring and merged with a monoenergetic electron beam that was guided in to and out of the ring using strong magnetic fields. Both neutral and positive fragments from the collision process were detected with surface barrier detectors. It was found that pure detachment completely dominates over those channels which involves breaking the molecular bond. The threshold energy for the detachment process was found to be 7 eV. The cross section rose from zero to a maximum of about 5 · 10-16 cm2 just below 30 eV, after which it remained essentially constant. The threshold region was carefully investigated in an attempt to find resonance structure arising from the possible existence of the doubly charged ion, CN2-. The statistical uncertainty in the data was, however, too large to conclusively prove or disprove the existence of such a resonance.

Dissociative recombination of the polyatomic ions D3O+ and H3O+ with electrons have been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Absolute cross sections have been determined from 0.001 eV to 0.25 eV center-of-mass energy for D3O+ and from 0.001 eV to 28 eV for H3O+. The cross sections are large (7.3×10−13 cm2 for D3O+ and 3.3×10−12 cm2 for H3O+ at 0.001 eV). At low energies, the cross sections for D3O+ are E−1 energy dependent whereas it is slightly steeper for H3O+. A similar E−1 energy dependence was also observed by Mul et al. [J. Phys. B 16, 3099 (1983)] with a merged electron-ion beam technique for both H3O+ and D3O+ and by Vejby-Christensen et al. [Astrophys. J. 483, 531 (1997)] with the ASTRID storage ring in Denmark, who presented relative cross sections for H3O+. A resonance has been observed around 11 eV for H3O+. It reflects an electron capture to Rydberg states converging to an excited ionic core. A similar structure was reported by Vejby-Christensen et al. Our absolute measurements are in fairly good agreement with those from Mul et al., which were first divided by 2 (Mitchell, 1999, private communication) and from Heppner et al. [Phys. Rev. A 13, 1000 (1976)] for H3O+. Thermal rates were deduced from the measured cross sections for electron temperatures ranging from 50 K to 30 000 K. At 300 K, the thermal rate is equal to 7.6×10−7 cm3 s−1 for H3O+ and to 3.5×10−7 cm3 s−1 for D3O+. Complete branching ratios for all the possible product channels have been determined from 0 eV to 0.005 eV center-of-mass energy for D3O+ and at 0 eV for H3O+, using a well-characterized transmission grid in front of an energy-sensitive surface-barrier detector. No isotope effect was observed within the experimental uncertainties. The three-body break-up channel OX+X+X (where X stands for H or D) is found to occur for 67%–70% of the dissociations. Water or heavy water is produced with an 18%–17% probability and the production of oxygen atoms is negligible. These results support the three-body break-up dominance already found by Vejby-Christensen et al. for the DR of H3O+ in a similar heavy-ion storage ring experiment. However, even if the general trend is the same for both storage rings, significant differences have been observed and will be discussed.