Description
Dissociative recombination (DR) of molecular ions is a key chemical process in the cold interstellar medium (ISM). DR affects the composition, charge state, and energy balance of such environments. Astrochemical models of the ISM require reliable total DR cross sections as well as knowledge of the chemical composition and excitation states of the neutral DR products. Theory cannot reliably provide these data.
We have systematically measured DR for many astrophysically relevant molecular ions utilizing the TSR storage ring at the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. We used the merged ion-electron beam technique combined with an energy- and position-sensitive imaging detector and are able to study DR down to plasma temperatures of 10 K. The DR count rate is used to obtain an absolute DR rate coefficient. Additionally we determine the masses of the DR products by measuring their kinetic energy. This allows us to assign particular DR fragmentation channels and to obtain their branching ratios. Moreover, the distribution of detected fragment distances provides information on the kinetic energy released in DR and thus also on the internal excitation of the DR products. All of this information is particularly important for understanding DR of heteronuclear polyatomic ions.
HCl and HF molecules were recently identified as potentially good tracers for molecular hydrogen in interstellar clouds [1,2]. To use these tracers the underlying chlorine and fluorine chemistry must be understood. Current astrochemical models, however, lack reliable DR data. To this end we have measured DR for HCl+, D2Cl+, HF+, D2F+, and CF+.
This work is supported in part by the Max Planck Society, NASA, and the NSF.
References:
[1] D.A. Neufeld & M.G. Wolfire 2009 ApJ 706 1594
[2] D.A. Neufeld et al 2010 A&A 518 5
Author
Oldrich Novotny
(Columbia Astrophysics Laboratory)
Co-authors
A. Wolf
(Max-Planck-Institut für Kernphysik, Heidelberg)
Arno Becker
(Max-Planck-Institut für Kernphysik, Heidelberg)
B. Yang
(Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, Peoples Republic of China, University of Chinese Academy of Sciences, Beijing 100049, Peoples Republic of China)
C. Krantz
(Max-Planck-Institut für Kernphysik, Heidelberg)
D. Schwalm
(Max-Planck-Institut fur Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany, Weizmann Institute of Science, Rehovot 76100, Israel)
D. W. Savin
(Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA)
H. Buhr
(Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany, Weizmann Institute of Science, Rehovot 76100, Israel)
H. Kreckel
J. Stutzel
(Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA)
K. Spruck
(Institut für Atom- und Molekülphysik, Gießen)
M. Hamberg
(Department of Physics, Stockholm University, AlbaNova, SE-106 91, Stockholm, Sweden)
W. Geppert
(Department of Physics, Stockholm University, AlbaNova, SE-106 91, Stockholm, Sweden)