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.

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.

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.

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.

The gas phase reactivity of the radical cation isomers H₂CNH˙+ (methanimine) and HCNH₂˙+ (aminomethylene) with propene (CH₃CHCH₂) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07–11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation. Experimental results have been merged with theoretical calculations to elucidate reaction pathways and structures of products. The H₂CNH˙+ isomer is over a factor two more reactive than HCNH₂˙+. A major channel from both isomers is production of protonated methanimine CH₂NH₂+via hydrogen-atom transfer reaction but, while H₂CNH˙+ additionally gives charge and proton transfer products, the HCNH₂˙+ isomer leads instead to protonated vinylimine CH₂CHCHNH₂+, produced alongside CH₃˙ radicals. The reactions have astrochemical implications in the build up of chemical complexity in both the interstellar medium and the hydrocarbon-rich atmospheres of planets and satellites.

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.