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- Senevirathne, Bethmini, 1982, et al.
(författare)
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Hydrogen atom mobility, kinetic isotope effects and tunneling on interstellar ices (I-h and ASW)
- 2017
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Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758. ; 6, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Transitions of a single H atom between local minima on the surfaces of crystalline ice (I-h) and amorphous solid water (ASW) are studied theoretically in the temperature range 4-25 K. Binding energies, barrier heights, transition rate constants and the kinetic isotope effect (KIE) with and without tunneling are calculated. Harmonic transition state theory is used to obtain the transition rate constants and tunneling is treated with the Wigner tunneling correction, Eckart barrier correction and harmonic quantum transition state theory (HQTST). The classical binding energies are smaller on I-h (<47 meV) than on ASW (<89 meV). Also the classical barrier heights are smaller on I-h (<14 meV) than on ASW (<69 meV) and distributed over a range of energies, in line with previous experimental observations. Similarly the vibrationally adiabatic ground state (VAG) barrier heights are smaller on I-h (<7 meV) than on ASW (<54 meV). The surface morphology strongly influences the well depths. Tunneling increases some of the transition rate constants substantially but has a much smaller effect on others. The average KIE for I-h is higher than for ASW for the same range of barrier heights. (C) 2017 Elsevier B.V. All rights reserved.
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| 2. |
- Wakelam, V., et al.
(författare)
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H2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations
- 2017
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Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758. ; 9, s. 1-36
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Tidskriftsartikel (refereegranskat)abstract
- Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H2 formation in a variety of interstellar environments. © 2017 Elsevier B.V.
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