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Träfflista för sökning "WFRF:(Andersson Thomas 1970 ) ;pers:(Semaniak J)"

Sökning: WFRF:(Andersson Thomas 1970 ) > Semaniak J

  • Resultat 1-3 av 3
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1.
  • Al-Khalili, A, et al. (författare)
  • Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5700-5708
  • Tidskriftsartikel (refereegranskat)abstract
    • Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.
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2.
  • Öjekull, Jenny, 1973, et al. (författare)
  • Dissociative recombination of ammonia clusters studied by storage ring experiments
  • 2006
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:19, s. 194306-
  • Tidskriftsartikel (refereegranskat)abstract
    • Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)(2), H+(NH3)(3), D+(ND3)(2), and D+(ND3)(3) in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)(2) and D+(ND3)(2) show no clear isotope effect. Dissociative recombination of X+(NX3)(2) (X=H or D) is dominated by the product channels 2NX(3)+X [0.95 +/- 0.02 for H+(NH3)(2) and 1.00 +/- 0.02 for D+(ND3)(2)]. Dissociative recombination of D+(ND3)(3) is dominated by the channels yielding three N-containing fragments (0.95 +/- 0.05).
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3.
  • Öjekull, Jenny, 1973, et al. (författare)
  • Dissociative recombination of NH4+ and ND4+ ions : Storage ring experiments and ab initio molecular dynamics
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:16, s. 7391-7399
  • 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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  • Resultat 1-3 av 3

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