Dissociative recombination of NH4+ and ND4+ ions: Storage ring experiments and ab initio molecular dynamics
2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 16, 7391-7399 p.Article in journal (Refereed) Published
The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
Place, publisher, year, edition, pages
2004. Vol. 120, no 16, 7391-7399 p.
Ammonia, Computer simulation, Dissociation, Energy transfer, Ion exchange, Ionization, Isotopes, Mathematical models, Molecular vibrations, Positive ions, Potential energy, Probability, Storage rings, Thermal effects
IdentifiersURN: urn:nbn:se:kth:diva-26366DOI: 10.1063/1.1669388ISI: 000220676000018ScopusID: 2-s2.0-2342470002OAI: oai:DiVA.org:kth-26366DiVA: diva2:372072
QC 201011242010-11-242010-11-242010-11-24Bibliographically approved