78 research outputs found
Evidence for two-electron processes in the mutual neutralization of O- with O+ and N+ at Subthermal Collision Energies
We have measured total absolute cross sections for the Mutual Neutralization
(MN) of O- with O+/N+. A fine resolution (of about 50 meV) in the kinetic
energy spectra of the product neutral atoms allows unique identification of the
atomic states participating in the mutual neutralization process. Cross
sections and branching ratios have also been calculated down to 1 meV
center-of-mass collision energy for these two systems with a multi-channel
Landau-Zener model and an asymptotic method for the ionic-covalent coupling
matrix elements. The importance of two-electron processes in one-electron
transfer is demonstrated by the dominant contribution of a core-excited
configuration of the nitrogen atom in N+ + O- collisions. This effect is
partially accounted for by introducing configuration mixing in the evaluation
of coupling matrix elements.Comment: 5 pages, 4 figure
Decay pathways for protonated and deprotonated adenine molecules
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Chemical Physics 151.4 (2019): 044306 and may be found at https://aip.scitation.org/doi/abs/10.1063/1.5109963We have measured fragment mass spectra and total destruction cross sections for protonated and deprotonated adenine following collisions with He at center-of-mass energies in the 20-240 eV range. Classical and ab initio molecular dynamics simulations are used to provide detailed information on the fragmentation pathways and suggest a range of alternative routes compared to those reported in earlier studies. These new pathways involve, for instance, losses of HNC molecules from protonated adenine and losses of NH2 or C3H2N2 from deprotonated adenine. The present results may be important to advance the understanding of how biomolecules may be formed and processed in various astrophysical environmentsThis work was supported by the Swedish Research Council (Constant Nos. 2017-00621, 2015-04990, 2016-04181, and 2018-04092). Furthermore, we acknowledge the European Joint on Theoretical Chemistry and Computational Modelling (INT-EJD-TCCM). We acknowledge the generous allocation of computer time at the Centro de Computacion Cientifica at the Universidad Autonoma de Madrid (CCC-UAM). This work was partially supported by Project No. CTQ2016-76061-P of the Spanish Ministerio de Economia y Competitividad (MINECO
Molecular dynamics studies of impulse driven reactions in molecules and molecular clusters
We have used molecular dynamics methods to study collisions between atoms and molecules or molecular clusters. We find that these collisions may yield highly reactive molecular fragments and efficient intracluster covalent bond-forming reactions in the cluster. There is a good agreement between our simulations and various experimental result
Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars
Recent radiative lifetime measurements accurate to +/- 5% (Stockett et al.
2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 8
even-parity and 62 odd-parity levels of Er II have been combined with new
branching fractions measured using a Fourier transform spectrometer (FTS) to
determine transition probabilities for 418 lines of Er II. This work moves Er
II onto the growing list of rare earth spectra with extensive and accurate
modern transition probability measurements using LIF plus FTS data. This
improved laboratory data set has been used to determine a new solar
photospheric Er abundance, log epsilon = 0.96 +/- 0.03 (sigma = 0.06 from 8
lines), a value in excellent agreement with the recommended meteoric abundance,
log epsilon = 0.95 +/- 0.03. Revised Er abundances have also been derived for
the r-process-rich metal-poor giant stars CS 22892-052, BD+17 3248, HD 221170,
HD 115444, and CS 31082-001. For these five stars the average Er/Eu abundance
ratio, = 0.42, is in very good agreement with the
solar-system r-process ratio. This study has further strengthened the finding
that r-process nucleosynthesis in the early Galaxy which enriched these
metal-poor stars yielded a very similar pattern to the r-process which enriched
later stars including the Sun.Comment: 20 pages, 4 tables, 10 figures; To be published in the Astrophysical
Journal Supplemen
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