An experimental investigation of the radiative lifetime of the metastable 4s24p4(3P)4d4D7/2 level in Kr II shows an unusual situation regarding the importance of an M2 depopulation channel. While the first order M1 and E2 channels are expected to contribute in a dominant way to the decay, the experimental result, obtained using a laser probing technique on a stored ion beam, tau = 0.57+/-0.03 s, is far too short to be due to these channels according to our relativistic multiconfiguration Dirac-Fock calculation. Only if second order contributions to the decay branches (including essentially the M2 contribution) are taken into account in the calculations could the unexpected short lifetime be explained.

Lifetime measurements of the metastable 3d D-2(3/2) level in singly charged calcium were performed using the newly developed violet diode laser operated in an external cavity arrangement. The laser was employed on stored ions at the CRYRING facility to optically pump the resonance line at 397 nm. In combination with laser probing at 866 nm this detection scheme gave the possibility to record the lifetime of this level. which has a radiative lifetime of about 1 s.

We report on a calculation of five lifetimes of metastable levels in Ar II, obtained with a relativistic Hartree-Fock method in which most of the intravalence correlation is represented within a configuration interaction scheme while core-valence correlation is described by a core-polarization model potential with a core-penetration corrective term. The quality of the calculation has been assessed through an experimental determination of the radiative lifetime of the metastable 3d 4F9/2 level. The experiment was performed with a laser probing technique on a stored ion beam at the CRYRING of Stockholm.

We have extended the laser probing technique at the CRYRING storage ring to measurement of the extremely long lifetime (28 s) of the metastable 3d2(3P)4s b 4P5/2 level in Ti II. The result obtained demonstrates the power of this method for investigation of such long-lived levels. This is the first experimental lifetime investigation of metastable states in Ti II.

We report on experimental transition probabilities for thirteen forbidden (Fe II) lines originating from three dierent metastable Feii levels. Radiative lifetimes have been measured of two metastable states by applying a laser probing technique on a stored ion beam. Branching ratios for the radiative decay channels, i.e. M1 and E2 transitions, are derived from observed intensity ratios of forbidden lines in astrophysical spectra and compared with theoretical data. The lifetimes and branching ratios are combined to derive absolute transition probabilities, A-values. We present the first experimental lifetime values for the two Fe II levels a 4 G9=2 and b 2 H11=2 and A-values for 13 forbidden transitions from a 6 S5=2, a 4 G9=2 and b 4 D7=2 in the optical region. A discrepancy between the measured and calculated values of the lifetime for the b 2 H11=2 level is discussed in terms of level mixing. We have used the code CIV3 to calculate transition probabilities of the a 6 D-a 6 S transitions. We have also studied observational branching ratios for lines from 5 other metastable Fe II levels and compared them to calculated values. A consistency in the deviation between calibrated observational intensity ratios and theoretical branching ratios for lines in a wider wavelength region supports the use of (Fe II) lines for determination of reddening.

We report an investigation into the three-body fragmentation of a triatomic molecule H2O via the process of dissociative recombination (DR) of H2O+. At 0-eV center-of-mass reaction energy two competing three-body fragmentation channels are available, both leading to the production of ground state H atoms H(S-2) but differing in the excitation state of the O atom fragment: O(P-3) and O(D-1). Using time- and position-sensitive detectors in a triple-coincidence experiment, the fragments from the DR reaction are monitored and their momentum vectors and angular distribution recorded. From these data we determine that during the recombination process, oxygen atoms are produced in the ratio of 3.5(0.5):1 for O(P-3):O(D-1), and find that the molecular geometry is not conserved and that the available reaction energy is randomly distributed between both hydrogen atoms. Quasiclassical trajectory calculations having the same initial starting conditions as those in the experiment have been carried out using calculated and measured H2O potential-energy surfaces, together with the knowledge of the various curve crossings, intersections, and estimations of the necessary coupling strengths. The results of these calculations, product state population distributions together with the geometries of the potential surfaces which contribute to the reaction, are compared to those observed in the experiment and allow questions to be answered on the dominance of three-body dissociation.

An experimental and theoretical investigation of lifetimes of metastable levels in La II has been performed. The experimentally obtained results using the laser probing of a stored ion beam were tau=5.2+/-0.2 s for the a(1)G(4) and tau=2.1+/-0.3 s for the b(1)D(2) levels. Within the error bars, the results are in good agreement with the relativistic Hartree-Fock calculations including core polarization.

Absolute cross sections for the production of H-+D+ in the collision of cold HD+ with electrons have been measured in the storage ring CRYRING at Manne Siegbahn Laboratory, Stockholm University in Stockholm. The magnitude of this cross section (similar to3x10(-19) cm(2) above threshold), as well as its interference pattern (14 peaks in the interaction energy region 0-16 eV) were found to be identical to that observed for the production of D-+H+, which was measured earlier in CRYRING.

We present the FERRUM Project, an international collaboration aiming at a production and evaluation of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of astrophysical relevance. The results obtained include measurements and calculations of permitted and forbidden lines of Fe II. The data have been applied to both emission and absorption lines in astrophysical spectra. We make comparisons between experimental, theoretical and astrophysical f-values. We give a general review of the various measurements, and discuss the UV8 multiplet of Fe II around 1610 Å in detail.

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.

The lifetime of two metastable levels in Fe+ has been measured by laser probing of a stored ion beam. In the dense spectrum of Fe+, the metastable levels a (6)S(5/2) and b (4)D(7/2) were selected and their lifetimes were determined to be 230 +/- 30 and 530 +/- 30 ms, respectively. The lifetimes are compared with previous theoretical results. Metastable lifetime measurements of Fe+ are of great importance for interpretation of spectra from astronomical objects. The present experiment opens for the possibilities to investigate lifetimes of metastable states in complex atomic ions, which have, so far, been unexplored.

The lowest-lying radiative state of barium chloride has been studied by laser-induced fluorescence in the near-infrared wavelength region. The A 2Π1/2 and A 2Π3/2 states have been investigated in time-resolved experiments using a Ti:Sapphire laser. The zero pressure radiative lifetime measured for the e-levels of BaCl was 107 ± 4 ns for the A 2Π1/2 state and 101 ± 6 ns for the A 2Π3/2 state. The discrepancy between the corresponding transition moments is discussed.

Dissociative recombination of vibrationally relaxed H2O+ ions with electrons has been studied in the heavy-ion storage ring CRYRING. Absolute cross-sections have been measured for collision energies between 0 eV and 30 eV. The energy dependence of the cross-section below 0.1 eV is found to be much steeper than the E-1 behaviour associated with the dominance of the direct recombination mechanism. Resonant structures found at 4 eV and 11 eV have been attributed to the electron capture to Rydberg states converging to electronically excited ionic states. Complete branching fractions for all dissociation channels have been measured at a collision energy of 0 eV. The dissociation process is dominated by three-body H + H + O breakup that occurs with a branching ratio of 0.71.