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Astron. Astrophys. 344, 1027-1033 (1999)

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Branching fractions in the dissociative recombination of NH[FORMULA] and NH[FORMULA] molecular ions

L. Vikor 1, A. Al-Khalili 1, H. Danared 2, N. Djuric 3, G.H. Dunn 3, M. Larsson 1, A. Le Padellec 1, S. Rosen 1 and M. af Ugglas 2

1 Department of Physics, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden
2 Manne Siegbahn Laboratory, Stockholm University, S-104 05 Stocholm, Sweden
3 JILA, University of Colorado, Campus Box 440, Boulder, CO 80309-0390, USA

Received 23 September 1998 / Accepted 4 February 1999

Abstract

Branching fractions in the dissociative recombination of NH[FORMULA] and NH[FORMULA] molecular ions with electrons were measured using the CRYRING heavy ion storage ring. We have determined complete branching fractions for NH[FORMULA] at 0 eV and 2 meV collision energies, and at 0 eV collision energy for NH[FORMULA]. We found the dissociative recombination of NH[FORMULA] to be dominated by the two body, `ammonia' channel. The branching fractions we obtained at 0 eV are 0.69 [FORMULA] 0.03 for the NH3 + H channel, and for the breakup into the NH2 + H2 and NH2 + 2H channels 0.10 [FORMULA] 0.02 and 0.21 [FORMULA] 0.03, respectively. The values we obtained for 2 meV are about the same as at 0 eV. For the NH[FORMULA] ion we obtained 0.66 [FORMULA] 0.01 for the three body N + H + H channel, 0.34 [FORMULA] 0.02 for NH + H, and no breakup into the N + H2 channel. Dissociative recombination of NH[FORMULA] and NH[FORMULA] is important as a potential source of some neutral molecules found in the interstellar clouds (NH3, NH2, and NH) and the measured branching fractions have important implications for modeling the chemistry of these clouds. We report also on the relative dissociative recombination cross sections for NH[FORMULA] and NH[FORMULA] for collision energies below 60 eV.

Key words: ISM: molecules – ISM: clouds – molecular processes

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© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999
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