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Interest in the observation and characterization of organic isomers in astronomical environments has grown rapidly with an increase in the sensitivity of detection techniques. Accurate modeling and interpretation of these environments require experimental isomer-specific reactivity and spectroscopic measurements. Given the abundance of formaldehyde (H 2 CO) in various astrophysical objects, the properties and reactivities of its cation isomers H 2 CO •+ and HCOH •+ are of significant interest. However, for the hydroxymethylene radical cation HCOH •+ (and its isotopologue DCOH •+ ), detailed reactivity studies have been limited by the lack of suitable experimental methods to generate this isomer with high purity. Here, potential approaches to the isomer-selective generation of HCOH •+ and DCOH •+ are characterized through differential reactivity measurements. While the dissociative photoionization of cyclopropanol (c-CH 2 CH 2 CHOH) is determined to be unsuitable, the dissociation of methanol- d 3 (CD 3 OH) allows for the formation of DCOH •+ with a fractional abundance of >99% at photon energies below 14.8 eV. These results will allow future spectroscopic and reactivity measurements of HCOH •+ /DCOH •+ to be conducted, laying the groundwork for future detection and incorporation into models of the interstellar medium.

We report a study on the reactive collision of S+(4S) with H2, HD, and D2 combining guided ion beam experiments and quantum-mechanical calculations. It is found that the reactive cross sections reflect the existence of two different mechanisms, one being spin-forbidden. Using different models, we demonstrate that the spin-forbidden pathway follows a complex mechanism involving three electronic states instead of two as previously thought. The good agreement between theory and experiment validates the methodology employed and allows us to fully understand the reaction mechanism. This study also provides new fundamental insights into the intersystem crossing process., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).)

Structural change of ions induced by collision with a neutral has been studied in a guided ion beam tandem mass spectrometer, using Time-Of-Flight measurements and SIMION simulation. The exothermic catalytic isomerization of HOC + to HCO + is used to explore the new methodology. Isomerization is catalyzed via a proton transport mechanism through the interplay of a neutral molecule, the catalyst. Four different potential catalysts, Ne, D 2 , CH 4, and C 18 O, were studied at different collision energies. SIMION simulation of the ion path and collision in the instrument leads to the highlight of a specific signature related to the catalytic isomerization in the time-of-flight spectra. This signature is used to identify the experimental conditions where isomerization takes place. Only C 18 O, at low collision energies, gives a clear signature of catalytic isomerization, and a quantitative estimate of the catalyzed isomerization cross-section and rate constant is derived. This new methodology is sensitive to clear presence of catalyzed isomerization and can be used in instruments designed for cross-section measurements, provided low collision energy is used and ion bunching is available., (© 2024 The Author(s). Journal of Mass Spectrometry published by John Wiley & Sons Ltd.)

A bio-responsive nanoparticle was formed by the directed self-assembly (DSA) of a hydrophobic NIR-fluorophore with poloxamer P 188 . Fluorophore emission was switched off when part of the nanoparticle, however upon stimulus induced nanoparticle dis-assembly the emission switched on. The emission quenching was shown to be due to fluorophore hydration and aggregation within the nanoparticle and the turn on response attributable to nanoparticle disassembly with embedding of the fluorophore within lipophilic environments. This was exploited for temporal and spatial live cell imaging with a measurable fluorescence response seen upon intracellular delivery of the fluorophore. The first dynamic response, seen within minutes, was from lipid droplets with other lipophilic regions such as the endoplasmic reticulum, nuclear membranes and secretory vacuoles imageable after hours. The high degree of fluorophore photostability facilitated continuous imaging for extended periods and the off to on switching facilitated the real-time observation of lipid droplet biogenesis as they emerged from the endoplasmic reticulum. With an in-depth understanding of the principles involved, further assembly controlling functional responses could be anticipated., Competing Interests: DFOS has a financial interest in patents filed and granted relating to NIR-fluorophores and processes for visual determination of tissue biology., (This journal is © The Royal Society of Chemistry.)