Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures
نویسندگان
چکیده
Understanding deuterium fractionation is currently one of the greatest challenges in astrochemistry. In this contribution deuteration experiments of the series CHn , 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 H2D + relaxed in collisions with H2. Preliminary results indicate that the ortho-to-para ratio of H2D + is substantially reduced in para-H2. This points at the important role of nuclear spin in deuterium fractionation, in particular at the destruction of ortho-H2D + in collisions with ortho-H2. More systematic LIR experiments are needed for a chemical model of deuterium fractionation including state-to-state modifications of the species involved.
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