David Osborne - Effect of isotopic content on the rate constants for the dissociative electron–ion recombination of N2H+

Version 1

      Publication Details (including relevant citation   information):

      International Journal of Mass   Spectrometry

        Volume 304, Issue 1, 15 June 2011, Pages 41-44


      The rate constants, αe, for dissociative   electron–ion recombination of various isotopic combinations of   N2H+ have been determined at 300 and 500 K   in a variable temperature flowing afterglow using a Langmuir   probe to determine the electron density. The values of   αe at 300 K are 2.77   (14N2H+), 2.12   (14N2D+), 2.31   (15N2H+) and 1.98   (15N2D+) × 10−7  cm3 s−1. The equivalent values at 500 K are   2.84, 2.33, 2.93, and 2.33 respectively. This has shown that the   greatest change occurs between H and D substitution   αe(14/15N2D+)/αe(14/15N2H+)   ∼ 0.765/0.857 at 300 K and 0.820/0.795 at 500 K respectively.   Values at 500 K are consistently larger than at 300 K. At both   temperatures, the rate constants with H substitution are larger   than with D substitution for both 14N and   15N. Values with 14N substitution are   larger than with 15N for both H and D. At 500 K, the   values are independent of whether the ion contains 14N   or 15N. Gas-phase 15N fractionation   enhancement is predicted in many regions of the interstellar   medium including cold and pre-stellar cores. The effect of this   fractionation on the recombination process is investigated. The   relevance to storage ring measurements of recombination rate   constants is considered and applications to the chemistry of the   interstellar medium are discussed.

      Address (URL): http://www.sciencedirect.com/science/article/pii/S1387380611001266