Hösten 2023 är jag räkneövningsledare på Mekanik I och laborationsassistent på Termodynamik som båda ingår i kursen Klassisk fysik på kandidatprogrammets första år. 

Jag har tidigare också varit laborationsassistent på Mekanik II, också det en delkurs i Klassisk fysik.

Det är nu vida känt att universum inte enbart består av atomer men också av över 2000 molekyler av olika slag. Med det följer behovet av att kartlägga hur dessa, ofta komplexa, molekyler bildas eftersom de tros agera som byggstenar för biomolekyler. Isomeri spelar en viktig roll då de utomjordiska miljöerna ofta är för kalla för att bistå med den energi som isomererna behöver för att konvertera sinsemellan. De kan då sägas effektivt bete sig som två olika molekyler.

I studiet av isomerer använder vi spektroskopiska mätinstrument runtom i Europa, vibrationsspektroskopi vid FELIX Laboratory, Nijmegen, rotationsspektroskopi vid unviersitetet i Bologna och reaktionsstudier vid SOLEIL synkrotron utanför Paris. Som komplement till mätningar används ab initio beräkningar för att understödja slutsatser utifrån observationer om isomerernas struktur och reaktivitet.

I urval från Stockholms universitets publikationsdatabas

• Isomers of ions in space and planetary atmospheres

  2022. David Sundelin.

  Avhandling (Lic)

  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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• Spectroscopic characterisation of the isomeric H₂NCH⁺ and H₂CNH⁺ radical cations

  2022. David Sundelin (et al.). Journal of Molecular Spectroscopy 387

  Artikel

  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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• Experimental and Computational Studies on the Reactivity of Methanimine Radical Cation (H₂CNH^+•) and its Isomer Aminomethylene (HCNH₂^+•) With C₂H₂

  2021. Vincent Richardson (et al.). Frontiers in Astronomy and Space Sciences 8

  Artikel

  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.

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• The reactivity of methanimine radical cation (H₂CNH^.+) and its isomer aminomethylene (HCNH₂^.+) with methane

  2021. V. Richardson (et al.). Chemical Physics Letters 775

  Artikel

  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.

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• The reactivity of methanimine radical cation (H₂CNH^•+) and its isomer aminomethylene (HCNH₂^•+) with C₂H₄

  2021. David Sundelin (et al.). Chemical Physics Letters 777

  Artikel

  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.

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• Laboratory gas-phase vibrational spectra of [C₃H₃]⁺ isomers and isotopologues by IRPD spectroscopy

  2020. Aravindh N. Marimuthu (et al.). Journal of Molecular Spectroscopy 374

  Artikel

  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.

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• Spacetime geometry of a wormhole modified BTZ black hole

  2018. David Sundelin.

  The unitarity problem for the BTZ black hole can possibly be solved by a coordinate transformation in which the event horizon is extended to a wormhole. In a model proposed by S.N. Solodukhin, this is done by the addition of a wormhole parameter $\lambda$ to the BTZ black hole line element. This thesis studies the changes in the spacetime geometry that comes with the addition of such a parameter. The focus of study are geodesic behaviour and possible bound states of waves. Investigating a possible source of the wormhole, the stress-energy tensor ansatz for a perfect fluid is also tested.

  The thesis concludes that there are notable changes to the spacetime depending on the presence of either a black hole or a wormhole. These changes includes orbital trajectories of geodesics and localized bound states of waves. The changes are most notable for $\lambda>1$ but also detectable for small parameter corrections. The wormhole spacetime can however not be generated by a simple addition of matter in a perfect fluid form.

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