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  • 1. Marimuthu, Aravindh N.
    et al.
    Sundelin, David
    Stockholm University, Faculty of Science, Department of Physics.
    Thorwirth, Sven
    Redlich, Britta
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Brünken, Sandra
    Laboratory gas-phase vibrational spectra of [C3H3]+ isomers and isotopologues by IRPD spectroscopy2020In: Journal of Molecular Spectroscopy, ISSN 0022-2852, E-ISSN 1096-083X, Vol. 374, article id 111377Article in journal (Refereed)
    Abstract [en]

    Gas phase vibrational spectra of [C3H3]+ isomers and their fully deuterated isotopologues measured in a cryogenic 22-pole ion trap are presented. The widely tunable free electron laser for infrared experiments, FELIX, was employed to cover the frequency range 500–2400 cm−1, complemented with an OPO/OPA system covering 2800–3400 cm−1. Spectral assignments for both the linear and cyclic isomeric form (H2C3H+ and c-C3H3+, respectively) are made based on various high-level computational studies. The effect of ion source conditions and different precursors (allene and propargyl chloride) for the preferential production of a specific isomer is discussed. The perturbation of the vibrational band position due to complexation with neon in the recorded infrared-predissociation (IRPD) spectra are also reported in this study.

  • 2. Richardson, V.
    et al.
    Alcaraz, C.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Polášek, M.
    Romanzin, C.
    Sundelin, David
    Stockholm University, Faculty of Science, Department of Physics.
    Thissen, R.
    Tosi, P.
    Žabka, J.
    Ascenzi, D.
    The reactivity of methanimine radical cation (H2CNH.+) and its isomer aminomethylene (HCNH2.+) with methane2021In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 775, article id 138611Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies are presented on the reactions of the isomeric radical cations H2CNH+ and HCNH2+ with CH4. Ionic isomers were generated selectively by VUV dissociative photoionization of azetidine and cyclopropylamine precursors respectively. Both exclusively give H2CNH2+ plus CH3 as products, but differences are observed related to a competition between stripping and complex-mediated H-transfer. Astrochemical implications for Titan’s atmosphere are briefly discussed, where the presence of methanimine (H2CNH), a key prebiotic molecule and a potential precursor for tholins, is proposed on the basis of atmospheric models and the observation of CH2NH2+ ions in Cassini mass spectrometric data.

  • 3. Richardson, Vincent
    et al.
    Ascenzi, Daniela
    Sundelin, David
    Stockholm University, Faculty of Science, Department of Physics.
    Alcaraz, Christian
    Romanzin, Claire
    Thissen, Roland
    Guillemin, Jean-Claude
    Polášek, Miroslav
    Tosi, Paolo
    Žabka, Jan
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental and Computational Studies on the Reactivity of Methanimine Radical Cation (H2CNH+•) and its Isomer Aminomethylene (HCNH2+•) With C2H22021In: Frontiers in Astronomy and Space Sciences, E-ISSN 2296-987X, Vol. 8, article id 752376Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies are presented on the reactivity of the radical cation isomers H2CNH+• (methanimine) and HCNH2+• (aminomethylene) with ethyne (C2H2). Selective isomer generation is performed via dissociative photoionization of suitable neutral precursors as well as via direct photoionization of methanimine. Reactive cross sections (in absolute scales) and product branching ratios are measured as a function of photon and collision energies. Differences between isomers’ reactivity are discussed in light of ab-initio calculations of reaction mechanisms. The major channels, for both isomers, are due to H atom elimination from covalently bound adducts to give [C3NH4]+. Theoretical calculations show that while for the reaction of HCNH2+• with acetylene any of the three lowest energy [C3NH4]+ isomers can form via barrierless and exothermic pathways, for the H2CNH+• reagent the only barrierless pathway is the one leading to the production of protonated vinyl cyanide (CH2CHCNH+), a prototypical branched nitrile species that has been proposed as a likely intermediate in star forming regions and in the atmosphere of Titan. The astrochemical implications of the results are briefly addressed.

  • 4.
    Sundelin, David
    Stockholm University, Faculty of Science, Department of Physics.
    Isomers of ions in space and planetary atmospheres2022Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ion chemistry has become increasingly important in the evolution of the chemical inventory of extraterrestrial environments. Isomers of ions have also come to play an important role as, in many instances, the cold environments in the interstellar medium and high layers of planet and satellite atmospheres do not supply enough energy to overcome isomerization barriers and the isomers effectively act as separate molecules. 

    In this licentiate thesis, several studies of the [CH3N]+ isomers are presented. Reactivity studies of the two isomers, the methanimine radical cation (H2CNH+) and aminomethylene (HCNH2+) with hydrocarbons C2H4, C2H2 and CH4, and IRPD spectroscopy of both species have been performed. Complimentary ab initio calculations aid in the determination of formation pathways of observed product channels and in the assignment of the vibrational bands seen in the IRPD spectrum.

    The results show that reaction pathways of the two isomers generally involve adduct formation followed by hydrogen ejection where the product or pathway is dependent on the ingoing reactant isomer. The IRPD spectrum allows identification of the different isomers via vibrational transitions. Isomer generation by electron ionization favours methanimine cation production with an abundance of 70% while with VUV photoionization it is possible to selectively produce isomers. It is concluded that isomerism must be considered when investigating the chemical environment of interstellar objects.

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  • 5.
    Sundelin, David
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Ascenzi, D.
    Richardson, V.
    Alcaraz, C.
    Polášek, M.
    Romanzin, C.
    Thissen, R.
    Tosi, P.
    Žabka, J.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    The reactivity of methanimine radical cation (H2CNH•+) and its isomer aminomethylene (HCNH2•+) with C2H42021In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 777, article id 138677Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies are presented on the reactivity of H2CNH'+ (methanimine) and HCNH2'+ (aminomethylene) with ethene (C2H4). Selective isomer generation is performed via dissociative photoionization of suitable neutral precursors and reactive cross sections and branching ratios are measured as a function of photon and collision energies. Differences between isomers' reactivity are discussed in light of ab-initio calculations on reaction mechanisms. The main products, for both isomers, are H-elimination, most likely occurring from covalently bound adducts (giving c-CH2CH2CHNH+/CH2NHCHCH2+) and H' atom transfer to yield H2CNH2+. The astrochemical implications of the results are briefly addressed.

  • 6.
    Sundelin, David
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Marimuthu, Aravindh N.
    Thorwirth, Sven
    Brünken, Sandra
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Spectroscopic characterisation of the isomeric H2NCH+ and H2CNH+ radical cations2022In: Journal of Molecular Spectroscopy, ISSN 0022-2852, E-ISSN 1096-083X, Vol. 387, article id 111640Article in journal (Refereed)
    Abstract [en]

    The vibrational transitions and the relative abundances of the two isomeric ions H2CNH+ and H2NCH+ generated through electron impact ionisation have been investigated in a noble gas tagging experiment. It could be shown that both species were formed with an abundance of 70 and 30% for H2NCH+ and H2CNH+, respectively. The obtained vibrational bands of the two species have been assigned to vibrational transitions through comparison with the results of ab initio calculations. These computations also predict both species to be moderately polar. The present investigations show that both isomers should be included in chemical model calculations of dark interstellar clouds, protoplanetary disks, star-forming regions as well as planetary atmospheres.

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