Bond-forming reactions of N22+ with C2H4, C2H6, C3H4 and C3H6

James D Fletcher,Michael A Parkes,Stephen D Price

doi:10.1016/j.ijms.2014.05.009

James D Fletcher, Michael A Parkes + Show 1 more

Open Access

https://doi.org/10.1016/j.ijms.2014.05.009

Copy DOI

Abstract

Mass spectrometry, coupled with position-sensitive coincidence detection, has been used to investigate the reactions of N22+ with various small hydrocarbon molecules (C2H4, C2H6, C3H4, c-C3H6 and n-C3H6) at collision energies below 10eV in the centre-of-mass frame. The reactivity, in each case, is dominated by electron transfer. However, in each collision system we also clearly identify products formed following the creation of new chemical bonds. These bond-forming reactions comprise two distinct classes: (i) hydride transfer reactions which initially form NnH+ (n=1, 2) and (ii) N+ transfer reactions which form monocationic products with CN bonds. These bond-forming reactions make a small (5–10%), but significant, contribution to the overall product ion yield in each collision system. The temporal and positional data recorded by our coincidence detection technique are used to construct scattering diagrams which reveal the mechanisms of the bond-forming reactions. For the hydride transfer process, the scattering diagrams reveal that H− is directly transferred from the hydrocarbon to N22+ at significant interspecies separations. For the hydride transfer reactions with C2H4, C2H6 and C3H4, we observe fragmentation of the nascent N2H+* to form NH++N. The N+ transfer reaction also proceeds by a direct mechanism: a single step involving N+/H exchange results in the formation of a singly-charged organic species containing a CN bond which is detected in coincidence with H+. The two general classes of bond-forming reactivity we observe in the reactions of N22+ with organic molecules may be relevant in the chemistry of energised environments rich in molecular nitrogen and hydrocarbon species, such as the atmosphere of Titan.

Highlights

Chemical modelling has predicted that N22+ is present in the nitrogen-rich ionosphere of Titan, the largest of Saturn’s moons [1]
We have identified two general types of bond-forming reaction, that accompany these electron transfer reactions: (i) H− transfer from the hydrocarbon to the dication forming a new N H bond and (ii) transfer of N+, resulting in the formation of two singlycharged species, one of which has a C N bond
The hydride transfer reactions can be further divided into processes which form NH+ and those which form N2H+

Summary

Introduction

Chemical modelling has predicted that N22+ is present in the nitrogen-rich ionosphere of Titan, the largest of Saturn’s moons [1]. The reactivity of N22+ with several of these neutral species has been documented in a recent review article by Dutuit et al [6] Summarising this experimental work, Lilensten et al have studied low energy collisions between N22+ and CH4, focusing on the kinetics of electron recombination and the identification of chemical reaction products [1,16]. The work reported in this article focuses on the dynamics of the bond-forming reactions which occur following collisions between N22+ and five low mass hydrocarbons: C2H4, C2H6, C3H4 and two isomers of C3H6 (propene and cyclopropane) In these collision systems, we clearly identify two types of bond-forming reaction which form pairs of singly charged ions: nitrogen (N) transfer and hydride (H−) transfer [1,16]. We note that the products of H− transfer are markedly more intense than those from N+ transfer in all the collision systems investigated, and a simple mechanistic explanation for this observation is presented

Experimental

Results and discussion

Hydride transfer

Conclusions