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1.
Faraday Discuss ; 165: 447-72, 2013.
Article in English | MEDLINE | ID: mdl-24601017

ABSTRACT

Recent laboratory and modelling studies have shown that reactive uptake of low molecular weight alpha-dicarbonyls such as glyoxal (GLY) by aerosols is a potentially significant source of secondary organic aerosol (SOA). However, previous studies disagree in the magnitude of the uptake of GLY, the mechanism involved and the physicochemical factors affecting particle formation. In this study, the chemistry of GLY with ammonium sulfate (AS) in both bulk laboratory solutions and in aerosol particles is investigated. For the first time, Aerosol Time of Flight Mass Spectrometry (ATOFMS), a single particle technique, is used together with offline (ESI-MS and LC-MS2) mass spectrometric techniques to investigate the change in composition of bulk solutions of GLY and AS resulting from aqueous photooxidation by OH and from ageing of the solutions in the dark. The mass spectral ions obtained in these laboratory studies were used as tracers of GLY uptake and chemistry in AS seed particles in a series of experiments carried out under dark and natural irradiated conditions at the outdoor European Photo-reactor (EUPHORE). Glyoxal oligomers formed were not detected by the ATOFMS, perhaps due to inefficient absorption at the laser wavelength. However, the presence of organic nitrogen compounds, formed by reaction of GLY with ammonia was confirmed, resulting in an increase in the absorption efficiency of the aerosol, and this increased the number of particles successfully ionised by the ATOFMS. A number of light absorbing organic nitrogen species, including 1H-imidazole, 1H-imidazole-2-carboxaldehyde, 2,2'-bis-imidazole and a glyoxal substituted 2,2'-bisimidazole, previously identified in aqueous laboratory solutions, were also identified in chamber aerosol and formed on atmospherically relevant timescales. An additional compound, predicted to be 1,2,5-oxadiazole, had an enhanced formation rate when the chamber was open and is predicted to be formed via a light activated pathway involving radical oxidation of ammonia to hydroxylamine, followed by subsequent reaction with glyoxal to form an intermediate glyoxime.


Subject(s)
Aerosols/chemistry , Ammonium Sulfate/chemistry , Glyoxal/chemistry , Mass Spectrometry/methods , Oxidation-Reduction
2.
Eur J Mass Spectrom (Chichester) ; 15(2): 91-104, 2009.
Article in English | MEDLINE | ID: mdl-19423896

ABSTRACT

Collision-induced activation of deprotonated trimethylamine N-oxide yields the two anions [N(CH(2))(3)](-) and [ON(CH(2))(2)](-) following losses of H(2)O and CH(4), respectively. These two anions decompose by minor losses of H(*) and H(2) when collisionally activated: no other fragmentations are noted. Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory indicate that these trigonal anions are stable, and should not rearrange following collisional activation. Collisional-induced charge stripping of the anions [N(CH(2))(3)](-) and [ON(CH(2))(2)](-), respectively, form N(CH(2))(3) and ON(CH(2))(2). Some of these neutrals are energised and undergo rearrangement and dissociation. From a consideration of experiment and theory, it is proposed (i) that energised N(CH(2))(3) may cyclise to form the 1-aziridinylcarbinyl radical. This species may ring open to CH(2)=NCH(2)CH(2) which then decomposes to CH(2)N and C(2)H(4) and (ii) energised ON(CH(2))(2) may undergo OC cyclisation followed by ring opening to energised CH(2)=NCH(2)O which may fragment to yield CH(2)N and CH(2)O.

3.
Rapid Commun Mass Spectrom ; 18(10): 1008-16, 2004.
Article in English | MEDLINE | ID: mdl-15150822

ABSTRACT

Neutrals MeCCCO, CCC(O)Me, PhCCCO and CCC(O)Ph have been made by neutralisation of [MeCCCO](+), [CCC(O)Me](-), [PhCCCO](+) and [CC(CO)Ph](-). Neutrals MeCCCO, CCC(O)Me and PhCCCO are stable for the microsecond duration of the neutralisation experiment. A joint experimental and theoretical study (energies calculated at the B3LYP/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory) suggests that the neutral radical CCC(O)Ph rearranges via a four-centred ipso radical cyclisation/ring opening to form the isomer PhCCCO in an exothermic reaction. (13)C labelling confirms that the rearrangement does not involve O migration. Some of the PhCCCO radicals formed in this reaction are sufficiently energised to effect decomposition to give PhCC and CO.

4.
J Mol Graph Model ; 21(5): 357-64, 2003 Mar.
Article in English | MEDLINE | ID: mdl-12543134

ABSTRACT

This paper is a modified version of a lecture which describes the synthesis, structure and reactivity of some neutral molecules of stellar significance. The neutrals are formed in the collision cell of a mass spectrometer following vertical Franck-Condon one electron oxidation of anions of known bond connectivity. Neutrals are characterised by conversion to positive ions and by extensive theoretical studies at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory. Four systems are considered in detail, viz (i) the formation of linear C(4) and its conversion to the rhombus C(4), (ii) linear C(5) and the atom scrambling of this system when energised, (iii) the stable cumulene oxide CCCCCO, and (iv) the elusive species O(2)C-CO. This paper is not intended to be a review of interstellar chemistry: examples are selected from our own work in this area.


Subject(s)
Astronomy , Ions/chemistry , Mass Spectrometry/instrumentation , Models, Molecular , Astronomical Phenomena , Carbon/chemistry , Computer Simulation , Extraterrestrial Environment , Molecular Structure
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