| 1. |
- Vigren, E., et al.
(författare)
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Collision-induced dissociation of ∼2-MeV O+3 and N+3 ions
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 87:5
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Tidskriftsartikel (refereegranskat)abstract
- We present a study into the collision-induced dissociation (possibly including electron stripping) of O-3(+) and N-3(+) with rest gas molecules (predominantly H-2) in the heavy-ion storage ring CRYRING. The projectile ions had kinetic energies of 1.96 MeV (O-3(+)) and 2.25 MeV (N-3(+)) and from the experimental data we could derive the relative importance of the channels that produce at least one neutral product fragment. The dominant type of fragmentation for both ions involves the production of a single neutral fragment, namely an individual atom. We also find pronounced dissimilarities when comparing the O-3(+) and N-3(+) results, which we link to the stronger chemical bonds in the nitrogen system.
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| 2. |
- Fogle, M., et al.
(författare)
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Electron-impact dissociation of XH2+ (X = B, C, N, O, F) : Absolute cross sections for production of XH+ and X+ fragment ions
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 82:4, s. 042720-
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Tidskriftsartikel (refereegranskat)abstract
- Absolute cross sections for electron-impact dissociation of XH2+ (X = B, C, N, O, F) producing XH+ and X+ ion fragments were measured in the 3- to 100-eV range using a crossed-electron-ion beams technique. Dissociative excitation of BD2+ and CH2+ producing B+ and C+, respectively, show a propensity toward a two-body dissociation while the remaining species all tend to show a three-body dissociation dynamic. The BD+ and CH+ dissociative excitation channels show a large resonant-type contribution to the cross sections at similar to 10eV. For the X+ fragment ion production cross sections, a clear dependence on the threshold energy, as it relates to the rate of rise in the cross section above threshold, is observed.
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| 3. |
- Fogle, M., et al.
(författare)
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Electron-impact dissociative excitation and ionization of N(2)D(+)
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:3, s. 032714-
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Tidskriftsartikel (refereegranskat)abstract
- Absolute cross sections for electron-impact dissociation of N(2)D(+) producing N(2)(+), ND(+), and N(+) ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N(2)(+) production dominates. The N(2)(+) + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N(2)(+), ND(+), and N(+) ion fragment production are comparable. The observance of the ND(+) and N(+) ion fragments indicate breaking of the N-N bond along certain dissociation channels.
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| 4. |
- Fogle, M., et al.
(författare)
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Electron-impact ionization of Be-like CIII, NIV, and OV
- 2008
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 175:2, s. 543-556
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Tidskriftsartikel (refereegranskat)abstract
- We present recent measurements of absolute electron-impact ionization cross sections for Be-like C III, N IV, and O V forming Li- like C IV, N V, and O VI. The measurements were taken using the crossed-beams apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in the ion beams. The measured ionization cross sections were compared with calculations using the R-matrix with pseudostates and distorted-wave theoretical methods. Best agreement is found with the R-matrix with pseudostates cross sections results that account for the metastable fractions inferred from the gas attenuation measurements. We present a set of recommended rate coefficients for electron-impact single ionization from the ground state and metastable term of each ion.
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| 5. |
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| 6. |
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| 7. |
- Bahati, E. M., et al.
(författare)
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Electron-impact dissociation of CD3+ and CH3+ ions producing CD2+, CH+ and C+ fragment ions
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79:5, s. 52703-
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Tidskriftsartikel (refereegranskat)abstract
- Using a crossed electron-ion beams method, we measured absolute cross sections for electron-impact dissociation of the CD3+ molecular ions producing CD2+ fragment ions and CH3+ ions yielding CH+ and C+ fragment ions over a collision energy range from a few eV up to 100 eV. The total experimental uncertainties are about 12% at the maximum of the curves of cross sections (peak of the cross section for the CH+ channel). The obtained results suggest important roles played by predissociation of bound states in the production of both the CH+ and C+ fragment ions. Good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+ fragments.
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| 8. |
- Hellberg, F, et al.
(författare)
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Investigating the breakup dynamics of dihydrogen sulfide ions recombining with electrons
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:22, s. 224314-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results concerning measurements of the dissociative recombination (DR) of dihydrogen sulfide ions. In combination with the ion storage ring CRYRING an imaging technique was used to investigate the breakup dynamics of the three-body channel in the DR of (SD2+)-S-32. The two energetically available product channels S(P-3)+2D(S-2) and S(D-1)+2D(S-2) were both populated, with a branching fraction of the ground-state channel of 0.6(0.1). Information about the angle between the two deuterium atoms upon dissociation was obtained together with information about how the available kinetic energy was distributed between the two light fragments. The recombination cross sections as functions of energy in the interval of 1 meV to 0.3 eV in the center-of-mass frame are presented for (SH2+)-S-34. The thermal rate coefficient for the DR of (SH2+)-S-34 was determined to be (4.8 +/- 1.0)x10(-7)(T/300)(-0.72 +/- 0.1) cm(3) s(-1) over this interval.
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| 9. |
- Thomas, R. D., et al.
(författare)
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Hot Water from Cold. The Dissociative Recombination of Water Cluster Ions
- 2010
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:14, s. 4843-4846
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of the Zundel cation D(5)O(2)(+) almost exclusively produces D + 2 D(2)O with a maximum kinetic energy release of 5.1 eV. An imaging technique is used to investigate the distribution of the available reaction energy among these products. Analysis shows that as much as 4 eV can be stored internally by the molecular fragments, with a preference for producing highly excited molecular fragments, and that the deuteron shows a nonrandom distribution of kinetic energies. A possible mechanism and the implications for these observations are addressed.
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| 10. |
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| 11. |
- Zhaunerchyk, V., et al.
(författare)
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Three-body breakup in the dissociative recombination of the covalent triatomic molecular ion O-3(+)
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:22, s. 223201-
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Tidskriftsartikel (refereegranskat)abstract
- We report the first observation of almost exclusive three-body breakup in the dissociative recombination of a covalent triatomic molecular ion O-3(+). The three-body channel, constituting about 94% of the total reactivity, has been investigated in detail. The atomic fragments are formed in only the first two electronic states, P-3 and D-1, while formation in the S-1 state has not been observed. The breakup predominantly proceeds through dissociative states with linear geometry.
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| 12. |
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| 13. |
- Thomas, Richard D., et al.
(författare)
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Dissociative recombination of LiH2
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 89:5, s. 050701-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report results regarding how LiH2+ fragments as a result of a low-energy collision with an electron (dissociative recombination), a reaction that contains only elements and particles created during the very first phase of the universe. The collision-energy-dependent reaction rate and cross sections show detailed structures, more so than predicted by theory, suggesting significant rovibrational coupling in the ion and a complex reaction surface. From the structure of the molecule, the reaction predominantly results in the formation of Li + H-2. However, 23% of the reaction flux leads to more interesting products, with 17% producing Li + 2H and 6% producing LiH + H. These last two channels break the strongest molecular bond in the system and, in the case of the latter channel, form a significantly weaker ionic bond. Possible reasons behind this interesting behavior are discussed, together with the interaction between the available reaction channels.
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| 14. |
- Vane, C. R., et al.
(författare)
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Electron-impact dissociation of CH2+ ions : Measurement of CH+ and C+ fragment ions
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:5, s. 52715-
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Tidskriftsartikel (refereegranskat)abstract
- Absolute cross sections for electron-impact dissociation of CH2+ producing CH+ and C+ fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross section peak. The cross sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C+ channel is relatively flat down to the lowest measured energy. Ionization cross sections for the CH2+ ion are also presented.
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| 15. |
- Zhaunerchyk, Vitali, et al.
(författare)
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Dissociative recombination study of PD2+ at CRYRING : absolute cross-section, chemical branching ratios and three-body fragmentation dynamics
- 2005
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 103:20, s. 2735-2745
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Tidskriftsartikel (refereegranskat)abstract
- The paper reports an investigation of the dissociative recombination of PD2+ at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ranging from 1 meV to 0.1 eV. The experiment performed has shown the dissociative recombination of PD2+ to be dominated by three-body break-up, with a branching ratio of about 78%. Competition between the available three-body channels producing the ground state, P(S-4), and the. first two excited states, P(D-2) and P(P-2), is observed. The formation of the first excited state dominates over the other two almost equally probable channels with about 75% of all three-body events. The results indicate that the kinetic energy released in the three-body break- up of PD2+ is randomly shared between the deuterium atoms. The intra-molecular angle on dissociation has also been investigated. A comparative analysis of the dissociative recombination dynamics for the two isovalent systems, PD2+ and NH2+, is undertaken.
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| 16. |
- Mujawamariya, M., et al.
(författare)
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Climate sensitivity of tropical trees along an elevation gradient in rwanda
- 2018
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 9:10
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Tidskriftsartikel (refereegranskat)abstract
- Elevation gradients offer excellent opportunities to explore the climate sensitivity of vegetation. Here, we investigated elevation patterns of structural, chemical, and physiological traits in tropical tree species along a 1700–2700 m elevation gradient in Rwanda, central Africa. Two early-successional (Polyscias fulva, Macaranga kilimandscharica) and two late-successional (Syzygium guineense, Carapa grandiflora) species that are abundant in the area and present along the entire gradient were investigated. We found that elevation patterns in leaf stomatal conductance (gs), transpiration (E), net photosynthesis (An), and water-use efficiency were highly season-dependent. In the wet season, there was no clear variation in gs or An with elevation, while E was lower at cooler high-elevation sites. In the dry season, gs, An, and E were all lower at drier low elevation sites. The leaf-to-air temperature difference was smallest in P. fulva, which also had the highest gs and E. Water-use efficiency (An/E) increased with elevation in the wet season, but not in the dry season. Leaf nutrient ratios indicated that trees at all sites are mostly P limited and the N:P ratio did not decrease with increasing elevation. Our finding of strongly decreased gas exchange at lower sites in the dry season suggests that both transpiration and primary production would decline in a climate with more pronounced dry periods. Furthermore, we showed that N limitation does not increase with elevation in the forests studied, as otherwise most commonly reported for tropical montane forests.
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