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Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures

Published online by Cambridge University Press:  21 March 2006

Stephan Schlemmer ,
Oskar Asvany ,
Edouard Hugo  and
Dieter Gerlich
Stephan Schlemmer
Affiliation:
I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany email: schlemmer@ph1.uni-koeln.de Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands
Oskar Asvany
Affiliation:
Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands
Edouard Hugo
Affiliation:
Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands
Dieter Gerlich
Affiliation:
Fakultät für Naturwissenschaften, Technische Universität Chemnitz, 09107 Chemnitz, Germany
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Abstract

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Understanding deuterium fractionation is currently one of the greatest challenges in astrochemistry. In this contribution deuteration experiments of the series CH$_n^+$, n=2–5, in a low temperature 22-pole ion trap are used to systematically test a simple chemical rule predicting which molecular ion undergoes deuterium exchange in collisions with HD. CH$_4^+$ turns out to be a problem case, where prediction fails. The method of laser induced reaction (LIR) is used to determine the population ratio of the lowest ortho-to-para states of H$_2$D$^+$ relaxed in collisions with H$_2$. Preliminary results indicate that the ortho-to-para ratio of H$_2$D$^+$ is substantially reduced in para-H$_2$. This points at the important role of nuclear spin in deuterium fractionation, in particular at the destruction of ortho-H$_2$D$^+$ in collisions with ortho-H$_2$. More systematic LIR experiments are needed for a chemical model of deuterium fractionation including state-to-state modifications of the species involved.

Keywords

astrochemistry — ISM: molecules — molecular processes
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 1 , Symposium S231: Astrochemistry: Recent Successes and Current Challenges , August 2005 , pp. 125 - 134
Copyright
2006 International Astronomical Union