| 1. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: Cross sections and branching ratios
- 2007
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127, s. 194301-194309
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the water cluster ions H+(H2O)3 and D+(D2O)3 with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H+(H2O)3 in the energy range of 0.001–0.8 eV, and relative cross sections have been measured for D+(D2O)3 in the energy range of 0.001–1.0 eV. The DR cross sections for H+(H2O)3 are larger than previously observed for H+(H2O)n (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H+(H2O)3 mainly results in the formation of 3H2O+H (probability of 0.95±0.05) and with a possible minor channel resulting in 2H2O+OH+H2 (0.05±0.05). The dominating channels for DR of D+(D2O)3 are 3D2O+D (0.88±0.03) and 2D2O+OD+D2 (0.09±0.02). The branching ratios are comparable to earlier DR results for H+(H2O)2 and D+(D2O)2, which gave 2X2O+X (X=H,D) with a probability of over 0.9.
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| 2. |
- Johansson, Sveneric, et al.
(författare)
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The FERRUM Project: New f-value Data for Fe II and Astrophysical Applications
- 2002
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Ingår i: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T100, s. 71-80
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Konferensbidrag (refereegranskat)abstract
- 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 Šin detail.
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| 3. |
- Någård, M. B., et al.
(författare)
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Dissociative recombination of D+(D2O)(2) water cluster ions with free electrons
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 117:11, s. 5264-5270
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the water cluster ion D+(D2O)(2) has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Cluster ions were injected into the ring and accelerated to an energy of 2.28 MeV. The stored ion beam was merged with an almost monoenergetic electron beam, and neutral fragments produced by DR were detected by an energy-sensitive surface barrier detector. The first experimental determinations of the absolute DR cross section and branching ratios for a cluster ion are reported. The cross section for the process D+(D2O)(2)+e(-) is large and reaches 6.10(-12) cm(2) at a low center-of-mass collision energy of 0.001 eV. The cross section has an E-1.19+/-0.02 dependence in the energy range 0.001-0.0052 eV, and a steeper slope with an E-1.70+/-0.12 dependence for E=0.052-0.324 eV. The general trends are similar to the results for previously studied molecular ions, but the cross section is higher in absolute numbers for the cluster ion. Thermal rate coefficients for electron temperatures of 50-2000 K are deduced from the cross section data and the rate coefficients are consequently also large. Branching ratios for the product channels are determined with a grid technique. Break-up into 2D(2)O+D is the dominating dissociation channel with a probability of 0.94+/-0.04. The channel resulting in the fragments D2O+OD+D-2 has a probability of 0.04+/-0.02, and the probability for formation of D3O+D2O is 0.02+/-0.03. The results are compared with data for molecular ions, and the cluster dissociation dynamics are discussed.
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| 4. |
- Hartman, Henrik, et al.
(författare)
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The FERRUM Project: Experimental transition probabilities of [Fe II] and astrophysical applications
- 2003
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 397:3, s. 1143-1149
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Tidskriftsartikel (refereegranskat)abstract
- We report on experimental transition probabilities for thirteenforbidden [Fe II] lines originating from three different metastable FeIi levels. Radiative lifetimes have been measured of two metastablestates by applying a laser probing technique on a stored ion beam.Branching ratios for the radiative decay channels, i.e. M1 and E2transitions, are derived from observed intensity ratios of forbiddenlines in astrophysical spectra and compared with theoretical data. Thelifetimes and branching ratios are combined to derive absolutetransition probabilities, A-values.We present the first experimental lifetime values for the two Fe IIlevels a4G9/2 and b2H11/2and A-values for 13 forbidden transitions froma6S5/2, a4G9/2 andb4D7/2 in the optical region. A discrepancybetween the measured and calculated values of the lifetime for theb2H11/2 level is discussed in terms of levelmixing. We have used the code CIV3 to calculate transitionprobabilities of the a6D-a6S transitions.We have also studied observational branching ratios for lines from 5other metastable Fe II levels and compared them to calculated values. Aconsistency in the deviation between calibrated observational intensityratios and theoretical branching ratios for lines in a wider wavelengthregion supports the use of [Fe II] lines for determination of reddening.
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| 5. |
- Rostohar, D, et al.
(författare)
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Experimental INvestigation of radiative decay rates of metastable levels in Eu II
- 2001
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Ingår i: Physica Scripta. - 0031-8949. ; 64, s. 237-237
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Rostohar, D, et al.
(författare)
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Lifetime measurements of Metastable States in Fe
- 2001
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Ingår i: Physical Review Letters. - 1079-7114. ; 86, s. 1466-1466
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Tidskriftsartikel (refereegranskat)abstract
- 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 6S5/2 and b 4D7/2 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.
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| 7. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of NH4+ and ND4+ ions : Storage ring experiments and ab initio molecular dynamics
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:16, s. 7391-7399
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Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
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| 8. |
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| 9. |
- Biemont, E, et al.
(författare)
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Importance of an M2 depopulating channel for a KrII metastable state
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:6, s. 063003-
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of the radiative lifetime of the metastable 4s(2)4p(4)(P-3)4d D-4(7/2) 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.
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| 10. |
- Derkatch, A., et al.
(författare)
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Lifetime measurements of the A (2)Pi state of BaCl using laser spectroscopy
- 2000
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 332:04-mar, s. 278-282
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Tidskriftsartikel (refereegranskat)abstract
- The lowest-lying radiative state of barium chloride has been studied by laser-induced fluorescence in the near-infrared wavelength region. The A (II1/2)-I-2 and A (II3/2)-I-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 (II1/2)-I-2 state and 101+/-6 ns for the A (II3/2)-I-2 state. The discrepancy between the corresponding transition moments is discussed.
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